Low-density, open-cell, soft, flexible, thermoplastic, absorbent foam and method of making foam

ABSTRACT

A soft, flexible, low-density, open-cell, thermoplastic, absorbent foam formed from a foam polymer formula including a balanced amount of a plasticizing agent and a surfactant in combination with a base resin. Thermoplastic elastomers can be added to the foam polymer formula to improve softness, flexibility, elasticity, and resiliency of the resulting foam. The surfactant may be either a single surfactant or a multi-surfactant system. The foam possesses a number of qualities, such as softness and strength, which render the foam particularly suitable for use in a variety of personal care products, medical products, and the like.

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/729,881, filed 05 Dec. 2003, the disclosure of which isincorporated by reference.

BACKGROUND OF THE INVENTION

This invention is directed to a low-density, open-cell, thermoplastic,absorbent foam that is soft and flexible. The foam can be made withbalanced amounts of one or more surfactants and a plasticizing agent ina foam polymer formula. Thermoplastic elastomers can be added to thefoam polymer formula to improve softness, flexibility, elasticity andresiliency. Some thermoplastic elastomers function as plasticizingagents.

Thermoplastic absorbent foam is made of polymer(s) that can be heated,formed and cooled repeatedly, typically commercially using a continuousplastic extrusion process. Thermoplastic absorbent foam can be used toproduce personal care products including, but not limited to, absorbentarticles such as disposable diapers, baby wipes, training pants,child-care pants, and other disposable garments; feminine-care productsincluding, but not limited to, sanitary napkins, wipes, menstrual pads,panty liners, panty shields, tampons, and tampon applicators; adult-careproducts including, but not limited to, wipes, pads, containers,incontinence products, and urinary shields. Besides use of such foam forpersonal care products, thermoplastic absorbent foam can also be used ina wide array of applications including a variety of professional andconsumer health and medical care products including, but not limited to,products for applying hot or cold therapy, hospital gowns, surgicaldrapes, bandages, wound dressings, wipes, covers, containers, filters,disposable garments and bed pads, medical absorbent garments, underpads,and the like, as well as clothing components, filters, thermal andacoustic insulation, shock and cushion absorbing products, athletic andrecreation products, construction and packaging uses, and service,industrial, and household products including, but not limited to,cleaning applications such as sponges and wipes for oleophilic and/orhydrophilic fluids; products for cleaning and disinfecting, and covers,filters, towels, bath tissue, and facial tissue; nonwoven roll goods;home-comfort products including pillows, pads, cushions, and masks andbody-care products such as washcloths, and products used to cleanse ortreat the skin. Low foam density and low modulus are required for highabsorbency, softness, flexibility, and in desired hand and fitaesthetics for applications such as diapers, incontinence products,smart system sensors, and other aforementioned products.

Extruded foams have a cellular structure, with cells defined by cellmembranes and struts. Struts are formed at the intersection of cellmembranes, with the cell membranes covering interconnecting cellularwindows between the struts. The thickness of cell struts is typically2-10 times greater than the thickness of cell membranes. Extruded foamsare typically produced with substantially closed cells. The open-cellcontent of closed-cell foams is generally less than 20%. Acceptableabsorbent foam has an open-cell structure, typically 50% or higher, asmeasured by ASTM D2856, and suitably has a controlled cell diameter.Specific cell size and cellular connectivity are adjusted to the desiredfunction, such as for high capillary fluid movement and high absorptioncapacity. Cell wall or membrane pores that connect cells are ofsufficient number and size to minimize viscous drag and flow resistanceto produce effective fluid transport and containment. Reticulated foamgenerally has a minimal number of cell windows or no cell windows (onlystruts) and, with sufficiently small enough pores, can effectivelytransport fluid. Such open-pore structures lend themselves to rapidfluid intake.

Processes are known for making open-cell foams, low-density foams,absorbent foams, and soft, resilient, elastomeric foams. One process forenhancing the open-cell formation in foam is described, for example, inU.S. Pat. No. 5,962,545. All of these foam qualities in a single foamwould be particularly desirable in a number of absorbent productapplications; however, it is difficult to produce such foam.

Foaming soft, flexible polymers, such as thermoplastic elastomers, tolow densities with absorbency is difficult to achieve. U.S. Pat. No.5,728,406 describes low-density, flexible, non-absorbent foam. Asdescribed in U.S. Pat. No. 6,451,865, heat-expandable thermoplasticparticles that encapsulate a heat-expandable gas or liquefied gas can beadded to produce such thermoplastic elastomer foam.

Plasticizing agents are sometimes used as cell openers in producingfoams. When used as cell openers, these plasticizing agents are added tothe thermoplastic foam polymer formula in minor amounts, as described inU.S. Pat. No. 6,071,580. More particularly, the plasticizing agent canact to increase cell expansion to produce a high expansion ratio. Whencells expand, membranes between cells thin and can become unstable,rupture, and can thereby create porous connections between cells. Inaddition, when thermoplastic polymer cools and with volumetriccontraction with crystallization, thin portions of the membrane canrupture enough to create additional connections or pores between cells,thereby creating open cells.

Although plasticizing agents act as softeners, the addition ofplasticizing agents makes foaming to low densities even more difficult.U.S. Pat. No. 6,653,360 describes a high density, essentiallyclosed-cell, non-absorbing foam containing a plasticizing agent andthermoplastic elastomer and additive such as a surfactant. Inparticular, plasticizing agents typically lower polymer melt viscositiesand lead to increasing melt drainage that causes foaming difficultieswith cell collapse. In fact, in certain manufacturing processes, such asfood packaging processes, plasticizing agents are used as defoamingagents.

There is a wide range of FDA-approved plasticizing agents available. Thecriterion for selecting a plasticizing agent for personal care productsincludes a wide range of properties including not only its softeningability but also temperature stability upon extrusion, resistance tomigration, cost, odor, biodegradability, and manufacturing and consumersafety. Typical plasticizing agents include citrates, phthalates,stearates, fats and oils. It is known that glycerol fatty acids, such asglycerol monostearate, stabilize cells by reducing the rate of gasdiffusion from the cell. However, such glycerol fatty acids are unableto provide sufficient wettability.

There is thus a need or desire for a soft, flexible, low-density,open-cell, thermoplastic, absorbent foam, and a method of making suchfoam.

SUMMARY OF THE INVENTION

This invention is directed to soft, flexible, low-density, open-cell,thermoplastic, absorbent foam, and a method of making such foam byforming a foam polymer formula that includes one or more surfactants anda plasticizing agent in combination with a base resin. Consequently, thefoam of the invention can include one or more surfactants and aplasticizing agent in combination with a base resin. The amount ofsurfactant and/or plasticizing agent can be adjusted in order to controlsoftness, open-cell content, and cellular size and structure of theresulting foam. A thermoplastic elastomer can be added to the foampolymer formula in addition to, or in place of, the plasticizing agentto enhance the resiliency, flexibility, softness, and elasticity of theresulting foam.

The open-cell content of the foam is about 50% or greater. Additionally,the absorbent foam may have about 5% or more closed cells, or about 10%or more closed cells, or about 15% or more closed cells to improveresiliency and/or compression resistance. The foam is low density, witha density of about 0.1 gram/cubic centimeter (g/cm³) or less, and issoft and flexible, with a bending modulus less than 6000 KPa at 1 mmdeflection, and an edge compression of about 1000 grams or less. Asanother measure of softness, flexibility, elasticity, and resiliency,the foam suitably has a compression resistance of about 20% compressionset or less. The addition of the surfactant and plasticizing agent tothe foam polymer formula also enhances the uniformity of celldistribution within the foam.

The foam is absorbent and remains suitably absorbent even after repeatedwashings. The surfactant permanence remains intact in the foam such thatabout 15% or less of the surfactant is washed off after soaking in waterfor 24 hours and, alternatively, the surface tension of the supernatantremains greater than about 40 dynes/centimeter, and with 0.9% NaClsaline has a saturated capacity of about 3 grams/gram or greater, asmeasured under a 0.5 psi (3.45 KPa) loading, and a fluid intake flux ofabout 1 ml/sec/in² (0.15 ml/sec/cm²) or greater upon the first insult,about 1 ml/sec/in² (0.15 ml/sec/cm²) or greater upon the second insult,and about 1 ml sec/in² (0.15 ml/sec/cm²) or greater upon the thirdinsult. Furthermore, the foam suitably has a vertical wicking height ofabout 5 cm or higher in 30 minutes. With viscous fluid, saturationcapacity is about 3 g/g or greater and retention capacity is about 1 g/gor greater.

The foam may be thin, but possesses considerable strength. Moreparticularly, the foam may have a basis weight of about 400 grams persquare meter or less, with an overall bulk, measured at a 0.02 psi(0.138 KPa) loading, of about 6 millimeters or less, and amachine-direction (MD) and cross-direction (CD) trap tear strength eachof about 300 grams or greater.

One method of making the foam includes formulating a foam polymerformula by including both a plasticizing agent and a surfactant incombination with a base resin, heating the foam polymer formula tocreate a polymer melt, utilizing a blowing agent, extruding the polymermelt, and foaming the polymer melt to a density of about 0.1 g/cm³ orless, to form an open-cell, soft, flexible, thermoplastic, absorbentfoam. Alternatively, rather than a single surfactant, a multi-componentsurfactant system can be included in the foam polymer formula. Unlikemany foam-forming processes, the method of the invention is anon-aqueous method.

Suitably, the surfactant can be included in the foam polymer formula inan amount between about 0.05% and about 10% by weight, of the foampolymer formula, and the plasticizing agent can be included in the foampolymer formula in an amount between about 0.5% and about 10% by weight,of the foam polymer formula.

The plasticizing agent is typically used to increase flexibility andsoftness in rigid polymers and can also create open-cell structure inthe resulting foam by increasing drainage. However, the addition of aplasticizing agent makes it more difficult to achieve low-density foam.According to this invention, it has been found that the addition of asurfactant enables foaming of a foam polymer formula to low densities,even when the foam polymer formula includes a plasticizing agent. Thebenefits derived from the use of a plasticizing agent in thelow-density, open-cell foam-forming process are particularly unexpected.Chemicals used as plasticizing agents sometimes are used as defoamingagents. By adding surfactant(s) to the plasticizing agent, thisinvention counteracts the negative impact of such plasticizing/defoamingchemicals for use in a foam-forming process.

As mentioned, the open-cell content of the foam can be controlled byadjusting the amount of the surfactant and/or plasticizing agent in thefoam polymer formula. More particularly, the balance between cellstabilization with the surfactant and enhanced drainage from theplasticizing agent enables control over the open-cell content. Thesurfactant also provides wettability to enable the resulting foam toabsorb fluid. It has been shown that introduction of certain surfactantsvia various processes can lead to a highly substantive surfactantpresent for continued wettability upon repeated washings. For example,use of HOSTASTAT® HS-1 and other surfactants have remained 95% (byweight) intact even after 24 hours of washing with water. Additionally,it has been found that a multi-component surfactant system can achieveequal or better foam formation at a lower dosage than a single-componentsurfactant system.

In certain embodiments, a thermoplastic elastomer can be included in thefoam polymer formula to improve softness, flexibility, resiliency, andelasticity of the resulting foam.

With the foregoing in mind, it is a feature and advantage of theinvention to provide a low-density, open-cell, thermoplastic, absorbentfoam that is soft and flexible, and a method of making such a foam inwhich the open-cell content can be controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of this invention will be betterunderstood from the following detailed description taken in conjunctionwith the drawings, wherein:

FIG. 1 is a photomicrograph of a cross-section of a foam, described inExample 1, taken by scanning electron microscopy. The photomicrographwas taken at a magnification of 15×.

FIG. 2 is a photomicrograph of a cross-section of a foam, described inExample 1, taken by scanning electron microscopy. The photomicrographwas taken at a magnification of 15×.

FIG. 3 is a photomicrograph of a cross-section of a foam, described inExample 1, taken by scanning electron microscopy. The photomicrographwas taken at a magnification of 15×.

FIGS. 4-12 are photomicrographs of foam samples described in Example 3,taken by optical microscopy. The photomicrographs were taken at amagnification of 20×.

FIG. 13 representatively shows a partially cut away top view of asaturated capacity tester.

FIG. 14 representatively shows a side view of a saturated capacitytester.

FIG. 15 representatively shows a rear view of a saturated capacitytester.

FIGS. 16A-16B representatively show a top view and a side view,respectively, of the test apparatus employed for the Fluid Intake FluxTest.

FIG. 17 is a photomicrograph of a cross-section of RYNEL® 562-Bpolyurethane absorbent medical-grade foam, taken by scanning electronmicroscopy. The photomicrograph was taken at a magnification of 45×.

FIG. 18 is a photomicrograph of a cross-section of GENPAK® polystyreneabsorbent meat tray foam, taken by scanning electron microscopy. Thephotomicrograph was taken at a magnification of 20×.

FIG. 19 schematically illustrates an apparatus used to position theVertical Wicking Fluid Flux Test, described herein.

FIGS. 20A and 20B illustrate an apparatus used to perform the BendingModulus Test, described herein.

FIG. 21 illustrates a tandem extrusion process useful to make the foam.

FIG. 22 illustrates a post-treatment process for the foam.

DEFINITIONS

Within the context of this specification, each term or phrase below willinclude the following meaning or meanings.

“Cell” refers to a cavity contained in foam. A cell is closed when thecell membrane surrounding the cavity or enclosed opening is notperforated and has all membranes intact. Cell connectivity occurs whenat least one wall of the cell membrane surrounding the cavity hasorifices or pores that connect to adjacent cells, such that an exchangeof fluid is possible between adjacent cells.

“Compression” refers to the process or result of pressing by applyingforce on an object, thereby increasing the density of the object.

“Elastomer” refers to material having elastomeric or rubbery properties.Elastomeric materials, such as thermoplastic elastomers, are generallycapable of recovering their shape after deformation when the deformingforce is removed. Specifically, as used herein, elastomeric is meant tobe that property of any material which upon application of an elongatingforce, permits that material to be stretchable to a stretched lengthwhich is at least about 25 percent greater than its relaxed length, andthat will cause the material to recover at least 40 percent of itselongation upon release of the stretching elongating force. Ahypothetical example which would satisfy this definition of anelastomeric material in the X-Y planar dimensions would be a one (1)inch (2.54 cm) sample of a material which is elongatable to at least1.25 inches (3.18 cm) and which, upon being elongated to 1.25 inches(3.18 cm) and released, will recover to a length of not more than 1.15inches (2.92 cm). Many elastomeric materials may be stretched by muchmore than 25 percent of their relaxed length, and many of these willrecover to substantially their original relaxed length upon release ofthe stretching, elongating force. In addition to a material beingelastomeric in the described X-Y planar dimensions of a structure,including a web or sheet, the material can be elastomeric in the Zplanar dimension. Specifically, when a structure is applied compression,it displays elastomeric properties and will essentially recover to itsoriginal position upon relaxation. Compression set is sometimes used todescribe such elastic recovery.

“Open cell” refers to any cell that has at least one broken or missingmembrane or a hole in a membrane.

“Plasticizing agent” refers to a chemical agent that can be added to arigid polymer to add flexibility to rigid polymers. Plasticizing agentstypically lower the glass transition temperature.

“Polymer” generally includes but is not limited to, homopolymers,copolymers, including block, graft, random and alternating copolymers,terpolymers, etc., and blends and modifications thereof. Furthermore,unless otherwise specifically limited, the term “polymer” shall includeall possible molecular geometrical configurations of the material. Theseconfigurations include, but are not limited to isotactic, syndiotacticand atactic symmetries.

“Surfactant” is a compound, such as detergents and wetting agents, thataffects the surface tension of fluids.

“Thermoplastic” is meant to describe a material that softens and/orflows when exposed to heat and which substantially returns to itsoriginal hardened condition when cooled to room temperature.

“Absorbent article” includes, but is not limited to, personal careabsorbent articles, medical absorbent articles, absorbent wipingarticles, as well as non-personal care absorbent articles includingfilters, masks, packaging absorbents, trash bags, stain removers,topical compositions, laundry soil/ink absorbers, detergentagglomerators, lipophilic fluid separators, cleaning devices, and thelike.

“Personal care absorbent article” includes, but is not limited to,absorbent articles such as disposable diapers, baby wipes, trainingpants, child-care pants, and other disposable garments; feminine-careproducts including sanitary napkins, wipes, menstrual pads, pantyliners, panty shields, interlabials, tampons, and tampon applicators;adult-care products including wipes, pads, containers, incontinenceproducts, and urinary shields; and the like.

“Medical absorbent article” includes a variety of professional andconsumer health-care products including, but not limited to, productsfor applying hot or cold therapy, hospital gowns, surgical drapes,bandages, wound dressings, covers, containers, filters, disposablegarments and bed pads, medical absorbent garments, gowns, underpads,wipes, and the like.

“Absorbent wiping article” includes facial tissue, towels such askitchen towels, disposable cutting sheets, away-from-home towels andwipers, wet-wipes, sponges, washcloths, bath tissue, and the like.

“Menses simulant” is a material that simulates the viscoelastic andother properties of menses, which is a “complex liquid.” As used herein,the phrase “menses simulant” or “complex liquid” describes a liquidgenerally characterized as being a viscoelastic fluid comprisingmultiple components having inhomogeneous physical and/or chemicalproperties. It is the inhomogeneous properties of the multiplecomponents that challenge the efficacy of an absorbent or adsorbentmaterial in the handling of complex liquids. In contrast with complexliquids, simple liquids, such as, for example, urine, physiologicalsaline, water, and the like, are generally characterized as having arelatively low viscosity and comprising one or more components havinghomogeneous physical and/or chemical properties. As a result of havinghomogeneous properties, the one or more components of simple liquidsbehave substantially similarly during absorption or adsorption, althoughsome components may be absorbed or adsorbed more readily than others.Although a complex liquid is generally characterized herein as includingspecific components having inhomogeneous properties, each specificcomponent of a complex liquid generally has homogeneous properties.Consider for example a representative complex body-liquid having threespecific components: red blood cells, blood protein molecules, and watermolecules. Upon examination, one skilled in the art could easilydistinguish between each of the three specific components according totheir generally inhomogeneous properties. Moreover, when examining aparticular specific component, such as the red blood cell component, oneskilled in the art could easily recognize the generally homogeneousproperties of the red blood cells. The “menses simulant” test fluid usedin this invention is composed of swine blood diluted with swine plasmato provide a hematocrit level of 35% (by volume). The fluid is furtherdescribed in U.S. Pat. No. 5,883,231, issued to Achter et al., which isincorporated by reference. A suitable device for determining thehematocrit level is a HEMATOSTAT-2 system, available from SeparationTechnology, Inc., a business having offices located in AltamonteSprings, Fla., U.S.A. A substantially equivalent system mayalternatively be employed.

“Viscous fluid” refers to a fluid having a viscosity greater than theviscosity of water, including such fluids as menses, menses simulant,fecal fluid, fecal fluid simulant, and the like.

These terms may be defined with additional language in the remainingportions of the specification.

DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the invention, a soft, flexible, low-density,open-cell, thermoplastic, absorbent foam can be made by forming a foampolymer formula that includes a plasticizing agent and one or moresurfactants in combination with a base resin. The plasticizing agentincluded in the foam polymer formula may further increase the softnessof the resulting foam and, optionally, to increase the open-cell contentand cell size of the resulting foam.

The foam of the invention possesses a number of desirable propertiesattributable to the balanced presence of both a plasticizing agent andsurfactant. The inclusion of the surfactant and plasticizing agent inthe foam polymer formula enhances softness, flexibility, absorbency, aswell as the uniformity of cell-size distribution within the foam. Asused herein, the term “foam polymer formula” refers to the compositionof the foam during the foam-forming process, whereas the term “foam”refers to a finished or formed state of the foam.

The soft, flexible, low-density, open-cell, thermoplastic, absorbentfoam is particularly suitable for use in a variety of absorbent articleapplications including, without limitation, personal care absorbentarticles, medical absorbent articles, and absorbent wiping articles.Personal care absorbent articles include, but are not limited to,absorbent articles such as disposable diapers, baby wipes, trainingpants, child-care pants, swimwear, and other disposable garments;feminine-care products including, but not limited to, sanitary napkins,wipes, menstrual pads, panty liners, panty shields, interlabials,tampons, and tampon applicators; adult-care products including, but notlimited to, wipes, pads, containers, incontinence products, and urinaryshields. Medical absorbent articles include professional and consumerhealth medical care products such as products for applying hot or coldtherapy, hospital gowns, surgical drapes, bandages, wound dressings,wipes, covers, containers, filters, disposable garments and bed pads,medical absorbent garments, underpads, and the like. Absorbent wipingarticles include facial tissue, washcloths, cleaning applicationsincluding sponges and wipes and impregnated wipes, towels such askitchen towels, disposable cutting sheets, away-from-home towels,wet-wipes, bath tissue, and the like. Besides use of such foam forpersonal care products, the foam can also be used in a wide array ofapplications including a variety of clothing components, andnon-personal care absorbent products including filters, masks, packagingabsorbents, trash bags, stain removers, topical compositions, laundrysoil/ink absorbers, detergent agglomerators, lipophilic fluidseparators, cleaning devices, athletic and recreation products, andconstruction and packaging uses. Additionally, because the foam isthermoplastic, the foam is also recyclable.

The open-cell content of the foam, which can be controlled by adjustingthe amount of surfactant and/or plasticizing agent included in the foampolymer formula, is suitably about 50% or greater, or about 70% orgreater, or about 80% or greater, as measured using ASTM D2856. The foamis low density, with a density of about 0.10 gram/cubic centimeter(g/cm³) or less, or about 0.07 g/cm³ or less, or about 0.04 g/cm³ orless and suitably at least about 0.02 g/cm³ (before any compression isapplied to meet specific packaging and/or in-use requirements), is softand flexible, and is resilient and elastic with an edge compression ofabout 250 grams or less, or about 100 grams or less, or about 35 gramsor less. The foam density is a measurement of bulk density, determinedusing ASTM D1622. Edge compression can be measured using the EdgeCompression Test Method, both of which are described in detail below.Softness, flexibility, elasticity, and resiliency are also demonstratedthrough compression set resistance. The foam of the invention suitablyhas a compression resistance of about 20% compression set or less, orabout 15% compression set or less, or about 7% compression set or less,as measured using ASTM D3575.

The foam remains suitably absorbent even after repeated washings. Thesurfactant permanence remains intact in the foam such that about 15% orless, or about 10% or less, or about 5% or less of the surfactant iswashed off after soaking in water for 24 hours. The SurfactantPermanence Test is described in detail below. An alternative measure ofthe surfactant permanence is the surface tension of the supernatant inthe same Surfactant Permanence Test. More particularly, the surfacetension of the supernatant remains greater than about 40dynes/centimeter, or greater than about 50 dynes/centimeter, or greaterthan about 60 dynes/centimeter.

The absorbent foam with 0.9% NaCl saline has a saturated capacity ofabout 3 grams/gram (g/g) or greater, or about 15 g/g or greater, orabout 30 g/g or greater, as measured under a 0.5 psi (3.45 KPa) loadusing the Saturated Capacity Test Method, described in detail below, anda fluid intake flux of about 1 ml/sec/in² (0.15 ml/sec/cm²) or greater,or about 3 ml/sec/in² (0.46 ml/sec/cm²) or greater, or about 5ml/sec/in² (0.77 ml/sec/cm²) or greater upon the first insult, about 1ml/sec/in² (0.15 ml/sec/cm 2) or greater, or about 3 ml/sec/in² (0.46ml/sec/cm²) or greater, or about 5 ml/sec/in² (0.77 ml/sec/cm²) orgreater upon the second insult, and about 1 ml/sec/in² (0.15 ml/sec/cm²)or greater, or about 3 ml/sec/in² (0.46 ml/sec/cm²) or greater, or about5 ml/sec/in² (0.77 ml/sec/cm²) or greater upon the third insult, usingthe Fluid Intake Flux Test or Modified Fluid Intatke Flux Test, alsodescribed in detail below. Furthermore, the foam has a vertical wickingheight of about 5 centimeters (cm) or higher, or about 7 cm or higher,or about 10 cm or higher, or about 15 cm or higher in 30 minutes, asmeasured with 0.9% NaCl saline solution using the Vertical Wicking Test,also described in detail below. With viscous fluid, saturation capacityis about 3 g/g or greater, or about 25 g/g or greater, and retentioncapacity is about 1 g/g or greater, or about 3 g/g or greater, or about8 g/g or greater as determined using the Viscous Fluid SaturationCapacity and Retention Capacity Test, also described in detail below.

The foam may have a vertical wicking fluid flux at zero height of atleast about 5 g/sec/m², or at least about 7 g/sec/m², or at least about10 g/sec/m², measured using the Vertical Wicking Fluid Flux Testdescribed herein. The foam may have a functional capacity greater thanabout 0.1 gram/cc, suitably greater than about 0.4 gram/cc, or about 0.1to about 1.0 gram/cc, measured using the Functional Capacity Testdescribed herein.

The thermoplastic absorbent foam may be thin, but possesses considerablestrength. More particularly, the foam may have a basis weight of about400 grams per square meter or less, with an overall bulk, measured at0.05 psi (0.345 KPa) loading, of about 6 millimeters or less. Suitably,the foam has a cross-direction (CD) trap tear strength of about 300grams or greater, or about 600 grams or greater, or about 1200 grams orgreater, and a machine-direction (MD) trap tear strength of about 300grams or greater, or about 600 grams or greater, or about 1200 grams orgreater. Overall bulk can be measured using the Foam Caliper Testdescribed herein. Trap tear MD/CD strength of the foam may be measuredusing ASTM D1117-14.

The foam may have a bending modulus of less than about 6000 KPa,suitably less than about 4000 KPa, or about 200 to about 2000 KPa, at 1mm deflection, measured using the Bending Modulus Test described herein.The foam may have a dry tensile strength of about 5 kg to about 15 kg,suitably about 8 kg to about 12 kg, or about 9 kg to about 10 kg,measured using the Dry Tensile Strength Test described herein The foammay have a wet tensile strength of about 5 kg to about 15 kg, suitablyabout 7 kg to about 12 kg, or about 8.5 kg to about 10 kg, measuredusing the Wet Tensile Strength Test described herein. The foam may havea Wet Tensile Loss of less than about 10%, suitably less than about 8%,measured by comparing dry and wet tensile strengths, as describedherein. The foam may have a static coefficient of friction of about 0.20to about 1.50, typically about 0.40 to about 1.0, measured using theCoefficient Of Friction Test described herein.

Any one or more of the foam properties disclosed herein may be presentin the foam of the invention.

The base resin, or starting material, included in the foam polymerformula used to make the foam of the invention can include any suitablethermoplastic polymer, or blend of thermoplastic polymers, or blend ofthermoplastic and non-thermoplastic polymers.

Examples of polymers, or base resins, suitable for use in the foampolymer formula include styrene polymers, such as polystyrene orpolystyrene copolymers or other alkenyl aromatic polymers; polyolefinsincluding homo or copolymers of olefins, such as polyethylene,polypropylene, polybutylene, etc.; polyesters, such as polyalkyleneterephthalate; and combinations thereof. A commercially availableexample of polystyrene resin is Dow STYRON® 685D, available from DowChemical Company in Midland, Mich., U.S.A.

Coagents and compatibilizers can be utilized for blending such resins.Crosslinking agents can also be employed to enhance mechanicalproperties, foamability and expansion. Crosslinking may be done byseveral means including electron beams or by chemical crosslinkingagents including organic peroxides. Use of polymer side groups,incorporation of chains within the polymer structure to prevent polymercrystallization, lowering of the glass transition temperature, loweringa given polymer's molecular weight distribution, adjusting melt flowstrength and viscous elastic properties including elongational viscosityof the polymer melt, block copolymerization, blending polymers, and useof polyolefin homopolymers and copolymers have all been used to improvefoam flexibility and foamability. Homopolymers can be engineered withelastic and crystalline areas. Syndiotactic, atactic and isotacticpolypropylenes, blends of such and other polymers can also be utilized.Suitable polyolefin resins include low, including linear low, medium andhigh-density polyethylene and polypropylene, which are normally madeusing Ziegler-Natta or Phillips catalysts and are relatively linear;generally more foamable are resins having branched polymer chains.Isotactic propylene homopolymers and blends are made usingmetallocene-based catalysts. Olefin elastomers are included.

Ethylene and α-olefin copolymers, made using either Ziegler-Natta or ametallocene catalyst, can produce soft, flexible foam havingextensibility. Polyethylene cross-linked with α-olefins and variousethylene ionomer resins can also be utilized. Use of ethyl-vinyl acetatecopolymers with other polyolefin-type resins can produce soft foam.Common modifiers for various polymers can also be reacted with chaingroups to obtain suitable functionality. Suitable alkenyl aromaticpolymers include alkenyl aromatic homopolymers and copolymers of alkenylaromatic compounds and copolymerizable ethylenically unsaturatedcomonomers including minor proportions of non-alkenyl aromatic polymersand blends of such. Ionomer resins can also be utilized.

Other polymers that may be employed include natural and syntheticorganic polymers including cellulosic polymers, methyl cellulose,polylactic acids, polyvinyl acids, polyacrylates, polycarbonates,starch-based polymers, polyetherimides, polyamides, polyesters,polymethylmethacrylates, and copolymer/polymer blends. Rubber-modifiedpolymers such as styrene elastomers, styrene/butadiene copolymers,ethylene elastomers, butadiene, and polybutylene resins,ethylene-propylene rubbers, EPDM, EPM, and other rubbery homopolymersand copolymers of such can be added to enhance softness and hand. Olefinelastomers can also be utilized for such purposes. Rubbers, includingnatural rubber, SBR, polybutadiene, ethylene propylene terpolymers, andvulcanized rubbers, including TPVs, can also be added to improverubber-like elasticity.

Thermoplastic foam absorbency can be enhanced by foaming withspontaneous hydrogels, commonly known as superabsorbents.Superabsorbents can include alkali metal salts of polyacrylic acids;polyacrylamides; polyvinyl alcohol; ethylene maleic anhydridecopolymers; polyvinyl ethers; hydroxypropylcellulose; polyvinylmorpholinone; polymers and copolymers of vinyl sulfonic acid,polyacrylates, polyacrylamides, polyvinyl pyridine; and the like. Othersuitable polymers include hydrolyzed acrylonitrile grafted starch,acrylic acid grafted starch, carboxy-methyl-cellulose, isobutylenemaleic anhydride copolymers, and mixtures thereof. Further suitablepolymers include inorganic polymers, such as polyphosphazene, and thelike. Furthermore, thermoplastic foam biodegradability and absorbencycan be enhanced by foaming with cellulose-based and starch-basedcomponents such as wood and/or vegetable fibrous pulp/flour.

In addition to any of these polymers, the foam polymer formula may also,or alternatively, include diblock, triblock, tetrablock, or othermulti-block thermoplastic elastomeric and/or flexible copolymers such aspolyolefin-based thermoplastic elastomers including random blockcopolymers including ethylene α-olefin copolymers; block copolymersincluding hydrogenated butadiene-isoprene-butadiene block copolymers;stereoblock polypropylenes; graft copolymers, includingethylene-propylene-diene terpolymer or ethylene-propylene-diene monomer(EPDM), ethylene-propylene random copolymers (EPM), ethylene propylenerubbers (EPR), ethylene vinyl acetate (EVA), and ethylene-methylacrylate (EMA); and styrenic block copolymers including diblock andtriblock copolymers such as styrene-isoprene-styrene (SIS),styrene-butadiene-styrene (SBS), styrene-isoprene-butadiene-styrene(SIBS), styrene-ethylene/butylene-styrene (SEBS), orstyrene-ethylene/propylene-styrene (SEPS), which may be obtained fromKraton Polymers of Belpre, Ohio, U.S.A., under the trade designationKRATON® elastomeric resin or from Dexco, a division of ExxonMobilChemical Company in Houston, Tex., U.S.A., under the trade designationVECTOR® (SIS and SBS polymers) or SEBS polymers as the SEPTON® series ofthermoplastic rubbers from Kuraray America, Inc. in New York, N.Y.,U.S.A.; blends of thermoplastic elastomers with dynamic vulcanizedelastomer-thermoplastic blends; thermoplastic polyether esterelastomers; ionomeric thermoplastic elastomers; thermoplastic elasticpolyurethanes, including those available from E. I. Du Pont de Nemoursin Wilmington, Del., U.S.A., under the trade name LYCRA® polyurethane,and ESTANE® available from Noveon, Inc. in Cleveland, Ohio, U.S.A.;thermoplastic elastic polyamides, including polyether block amidesavailable from ATOFINA Chemicals, Inc. in Philadelphia, Pa., U.S.A.,under the trade name PEBAX® polyether block amide; thermoplastic elasticpolyesters, including those available from E. I. Du Pont de NemoursCompany, under the trade name HYTREL®, and ARNITEL® from DSM EngineeringPlastics of Evansville, Ind., U.S.A., and single-site ormetallocene-catalyzed polyolefins having a density of less than about0.89 grams/cubic centimeter such as metallocene polyethylene resins,available from Dow Chemical Company in Midland, Mich., U.S.A. under thetrade name AFFINITY™; and combinations thereof.

As used herein, a tri-block copolymer has an ABA structure where the Arepresents several repeat units of type A, and B represents severalrepeat units of type B. As mentioned above, several examples of styrenicblock copolymers are SBS, SIS, SIBS, SEBS, and SEPS. In these copolymersthe A blocks are polystyrene and the B blocks are the rubbery component.Generally these triblock copolymers have molecular weights that can varyfrom the low thousands to hundreds of thousands and the styrene contentcan range from 5% to 75% based on the weight of the triblock copolymer.A diblock copolymer is similar to the triblock but is of an ABstructure. Suitable diblocks include styrene-isoprene diblocks, whichhave a molecular weight of approximately one-half of the triblockmolecular weight and having the same ratio of A blocks to B blocks.Diblocks with a different ratio of A to B blocks or a molecular weightlarger or greater than one-half of triblock copolymers may be suitablefor improving the foam polymer formula for producing low-density, soft,flexible, absorbent foam via polymer extrusion.

As illustrated in Examples 4 and 5 below, it may be particularlybeneficial to include a thermoplastic elastomer having a high diblockcontent and high molecular weight as part of the foam polymer formula toextrude low-density, soft, flexible, resilient, absorbent, thermoplasticfoam. For example, the thermoplastic elastomer may have a diblockcontent between about 50% and about 80%, by weight, of the totalthermoplastic elastomer weight.

KRATON® products have been shown to act as a discontinuous phase instyrenic-based foams and act as cell-opener generators when used insmall amounts. The amount of KRATON® polymers used in the foam polymerformula as a whole in the foam of the invention is of such a largemagnitude that the cell-opener effect is negligible compared to theresiliency, flexibility, elasticity, and softness imparted.

Suitably, the foam polymer formula includes up to about 90%, by weight,of polystyrene, and at least 10%, by weight, of thermoplastic elastomer.More particularly, the foam polymer formula may include between about45% and about 90%, by weight, of polystyrene, and between about 10% andabout 55%, by weight, of thermoplastic elastomer. Alternatively, thefoam polymer formula may include between about 50% and about 80%, byweight, of polystyrene, and between about 20% and about 50%, by weight,of thermoplastic elastomer. In one embodiment, for example, the foampolymer formula may include equal amounts of polystyrene andthermoplastic elastomer.

In another embodiment, the foam polymer formula may include about 40% toabout 80% by weight polystyrene and about 20% to about 60% by weightthermoplastic elastomer. In another embodiment, the foam polymer formulamay include about 50% to about 70% by weight polystyrene and about 30%to about 50% by weight thermoplastic elastomer.

In accordance with the invention, a plasticizing agent can be includedin the foam polymer formula. A plasticizing agent is a chemical agentthat imparts flexibility, stretchability and workability. The type ofplasticizing agent has an influence on foam gel properties, blowingagent migration resistance, cellular structure, including the fine cellsize, and number of open cells. Typically plasticizing agents are of lowmolecular weight. The increase in polymer chain mobility and free volumecaused by incorporation of a plasticizing agent typically results in aTg decrease, and plasticizing agent effectiveness is often characterizedby this measurement. Petroleum-based oils, fatty acids, and esters arecommonly used and act as external plasticizing agents or solventsbecause they do not chemically bond to the polymer yet remain intact inthe polymer matrix upon crystallization.

The plasticizing agent increases cell connectivity by thinning membranesbetween cells to the point of creating porous connections between cells;thus, the plasticizing agent increases open-cell content. Suitably, theplasticizing agent is included in an amount between about 0.5% and about10%, or between about 1% and about 10%, by weight, of the foam polymerformula. The plasticizing agent is gradually and carefully metered inincreasing concentration into the foam polymer formula during thefoaming process because too much plasticizing agent added at oncecreates cellular instability, resulting in cellular collapse.

Examples of suitable plasticizing agents include polyethylene, ethylenevinyl acetate, mineral oil, palm oil, waxes, esters based on alcoholsand organic acids, naphthalene oil, paraffin oil, and combinationsthereof. A commercially available example of a suitable plasticizingagent is a small-chain polyethylene that is produced as a catalyticpolymerization of ethylene; because of its low molecular weight it isoften referred to as a “wax.” This low-density, highly branchedpolyethylene “wax” is available from Eastman Chemical Company ofKingsport, Tenn., U.S.A., under the trade designation EPOLENE® C-10.

In order for the foam to be used in personal care and medical productapplications and many absorbent wiping articles and non-personal carearticles, the foam must meet stringent chemical and safety guidelines. Anumber of plasticizing agents are FDA-approved for use in packagingmaterials. These plasticizing agents include: acetyl tributyl citrate;acetyl triethyl citrate; p-tert-butylphenyl salicylate; butyl stearate;butylphthalyl butyl glycolate; dibutyl sebacate; di-(2-ethylhexyl)phthalate; diethyl phthalate; diisobutyl adipate; diisooctyl phthalate;diphenyl-2-ethylhexyl phosphate; epoxidized soybean oil; ethylphthalylethyl glycolate; glycerol monooleate; monoisopropyl citrate; mono-, di-,and tristearyl citrate; triacetin (glycerol triacetate); triethylcitrate; and 3-(2-xenoyl)-1,2-epoxypropane.

In certain embodiments, the same material used as the thermoplasticelastomer may also be used as the plasticizing agent. For example, theKRATON® polymers, described above, may be used as a thermoplasticelastomer and/or a plasticizing agent. In which case, the foam polymerformula may include between about 10% and about 50%, by weight, of asingle composition that acts as both a thermoplastic elastomer and aplasticizing agent. Described in an alternative manner, the foam may beformed without a plasticizing agent per se; in which case, the foampolymer formula may include between about 10% and about 50%, by weight,of the thermoplastic elastomer. An example of such a composition isSample 2a in Example 1, below.

Foaming of soft, flexible polymers, such as thermoplastic elastomers, toa low density is difficult to achieve. The addition of a plasticizingagent makes foaming to low densities even more difficult to achieve. Themethod of the invention overcomes this difficulty through the inclusionof a surfactant in the foam polymer formula. The surfactant stabilizesthe cells, thereby counteracting cellular collapse while retaining anopen-cell structure. This stabilization of the cells creates celluniformity and control of cell structure. In addition to enablingfoaming of plasticized thermoplastic elastomer polymer containing foamformulations to low densities, the surfactant also provides wettabilityto enable the resulting foam to absorb fluid.

While it is not intended to limit the invention to a particular theory,it is believed that improved cell stabilization is achieved via the useof surfactant in a foam polymer formula containing a plasticizing agent.The addition of a plasticizing agent makes foaming to low densities evenmore difficult to achieve. Plasticizing agents such as waxes, oils,silicone defoamers, and small particulates at low addition providelocalized surface tension reduction in the foam cell membrane, whichcauses rupturing and premature cellular collapse or coalescence. Themethod of the invention overcomes this difficulty through the additionof surfactant to the foam polymer formula which counteractsthermodynamic and kinetic instabilities of bubble formation in thepolymer melt. The surfactant stabilizes the cells, thereby counteractingcellular collapse caused by the plasticizing agent. This stabilizationof the cells creates cell uniformity in terms of cell size and cell sizedistribution and thereby allows control of cell structure. Since thesurfactant is a surface active agent, it lowers the surface orinterfacial tension and thus assists bubble formation. A decreasedsurface tension reduces the pressure differential required to maintain abubble of a certain size, reduces the pressure difference betweenbubbles of different sizes, reduces the free energy required to maintaina given interfacial area, and thus increases the bubble nucleation rate.As Gibbs theorem explains, a surfactant combats excessive thinning ofcell membranes and restores surfactant concentration to the surface andthereby acts as a stabilizing factor; however, a surfactant does notrestore liquid to the film, which results in a lack of self-repair. TheMarangoni effect describes surface flow of dragging underlying layers ofliquid to restore film thickness, which enhances film elasticity andresilience and thus counters cellular coalescence. This again is astabilizer. Assuming the credence of these two mechanisms, a surfactantwould be most effective if it is designed so that the Marangoni effectdominates the foam polymer formula, for if the Gibbs effect dominates,the diffusion rate would be too high and self-repair would not occur.Therefore the addition of surfactant acts as a “buffer” or “stabilizer”to control surface tension and with control of temperature, which alsoaffects surface tension, melt viscosity and melt strength, bubblestability can occur so that cells form in the thermoplastic melt. Thiseffect is offset by lowering the surface tension forces that hold thepolymer matrix together.

Bubble walls typically drain due to gravity and capillary forces. Suchdrainage thins the walls before the cell struts are sufficientlyhardened, which leads to cell collapse. La Place and Young proposed thatcapillary pressure at the junction of two or more ribs is lower, therebycreating flow from the membrane to the ribs and, consequently, thinning.With a sufficient amount of surfactant molecules arranged preferentiallyto migrate to the surface of the film membrane, the presence ofsurfactant at the membrane's thin film surfaces provides resistance todrainage of the molten plastic. If the film layer is sufficiently thick,such as in a foam membrane, it can be further stabilized by an ionicdouble layer of molecules resulting from orientation of ionicsurfactants. Both nonionic and ionic surfactants can exhibit anotherstabilizing force if the membrane is sufficiently thin. This would bedone by the alignment of surfactant tails to create a bi-layerstructure, such as found in biological cells, that is held together viaVan der Waals forces and thus stabilizes the foam membrane.

(References: Polymeric Foams, edited by Daniel Klempner and Kurt Frisch,Hanser Publishers, 1991; and Foam Extrusion, edited by S. T. Lee,Technomic Publishing Co., Inc., 2000.)

The surfactant is thought to also provide resistance to diffusion of thegas from the cell to the surroundings, which also aids in resistingcollapse. The reduced gas permeability due to the drainage resistance isrelated to the degree the surfactant can pack into the bubble's filmsurface and explains the difference between the performances of thevarious surfactants. This reduced rate of diffusion allows sufficientcooling for strut formation to prevent coalescence. The surfactant doesnot need to prevent drainage, but simply slows it sufficiently so thatthe cell struts are substantially hardened thereby preventing cellcoalescence. In general terms, it is expected that surfactants that arehighly mobile in the melt, highly surface active, and can pack tightlyand prevent membrane drainage will provide the best cell stabilization.

The surfactant may be a single surfactant, or a multi-componentsurfactant system. A multi-component surfactant system is a combinationof two or more surfactants. It has been found that certainmulti-component surfactant systems can achieve equal or better foamformation at a lower dosage than certain single-component surfactantsystems. Example 3, below, illustrates the effects of adding variousdosages of surfactant and surfactant mixtures to a polymer blend. Forexample, in the samples tested, the two-component surfactant foams haddensities comparable to foam made with over three times the amount of asingle-surfactant system. Surfactant is a costly component in the foampolymer formula. The use of certain multi-component surfactant systemscan be used to achieve foam having comparable foam properties at a lowercost than foam that includes three times as much surfactant.

The surfactant can be included in the foam polymer formula in an amountbetween about 0.05% and about 10%, or between about 0.1% and about 5%,by weight, of the foam polymer formula. In an embodiment in which thesurfactant is a multi-component surfactant system, the total of allsurfactants can be included in the foam polymer formula in an amountbetween about 0.05% and about 8.0%, or between about 0.1% and about3.0%, by weight, of the foam polymer formula. Examples of suitablesurfactants include cationic, anionic, amphoteric, and nonionicsurfactants. Anionic surfactants include the alkylsulfonates. Examplesof commercially available surfactants include HOSTASTAT® HS-1, availablefrom Clariant Corporation in Winchester, Va., U.S.A.; Cognis EMEREST®2650, Cognis EMEREST® 2648, and Cognis EMEREST® 3712, each availablefrom Cognis Corporation in Cincinnati, Ohio, U.S.A.; and Dow Coming 193,available from Dow Chemical Company in Midland, Mich., U.S.A. Alkylsulfonates are quite effective; however, use of this class ofsurfactants in certain applications may be limited because of productsafety. Some combinations offer unexpected benefits where the alkylsulfonate is added at a substantially lower level in conjunction withanother surfactant to yield good foaming and wettability. In oneembodiment, for example, the surfactant can be added to the foam polymerformula in a gaseous phase, such as through the use of a blowing agentsuch as supercritical carbon dioxide. One benefit of using a gaseoussurfactant is that the surfactant can fully penetrate and beincorporated into the polymer matrix, which can improve substantivityand thereby reduce surfactant fugitivity to enhance the foam's permanentwettability.

The balance between cell stabilization of the surfactant and theenhanced melt drainage from the plasticizing agent enables control overthe open-cell content of the resulting foam. More particularly, theamount of surfactant can be adjusted to counteract the effects of theplasticizing agent, and/or the amount of the plasticizing agent can beadjusted to counteract the effects of the surfactant. For example, ifthe plasticizing agent is included in the foam polymer formula in anamount between about 0.5% and about 5%, by weight, of the foam polymerformula, then the surfactant should be included in the foam polymerformula in an amount between about 0.5% and about 5%, by weight, of thefoam polymer formula. Similarly, if the plasticizing agent is includedin the foam polymer formula in an amount between about 5% and about 10%,by weight, of the foam polymer formula, then the surfactant should beincluded in the foam polymer formula in an amount between about 2% andabout 10%, by weight, of the foam polymer formula. In addition, thepolymer resin melt flow index can be adjusted to offset the plasticizingagent's effect.

Other additives can be included in the foam polymer formula to enhancethe properties of the resulting foam. For example, a nucleant can beadded to improve foam gas bubble formation in the foam polymer formula.Examples of suitable nucleants include talc, magnesium carbonate,nanoclay, silica, calcium carbonate, modified nucleant complexes, andcombinations thereof. An example of a commercially available nucleant isa nanoclay available under the trade name CLOISITE® 20A, from SouthernClay Products, Inc. in Gonzales, Tex., U.S.A. The nucleant can be addedto the foam polymer formula in an amount between about 0.1% and about5%, by weight, of the foam polymer formula. Nucleants, or nucleatingagents, are described in greater detail below.

A blowing agent, described in greater detail below, can be added to thefoam polymer formula to aid in the foaming process. Blowing agents canbe compounds that decompose at extrusion temperatures to release largevolumes of gas, volatile liquids such as refrigerants and hydrocarbons,or ambient gases such as nitrogen and carbon dioxide, or water, orcombinations thereof. A blowing agent can be added to the foam polymerformula in an amount between about 1% and about 10%, by weight, of thefoam polymer formula.

Once the foam polymer formula is mixed and formed, including theplasticizing agent, the surfactant, and any other additives, the foampolymer formula is heated and mixed, suitably to a temperature betweenabout 100 and about 500 degrees Celsius, to create a polymer melt. Theplasticizing agent reduces elongational viscosity of the polymer melt,which leads to foaming difficulties. However, the surfactant mediatesthe impact of the plasticizing agent on the viscosity, thereby providingcontrol over the open-cell content of the resulting foam. Also, asmentioned, the polymer resin melt index can be adjusted to offset theplasticizing agent's effect.

The polymer melt can be foamed using any suitable foaming techniqueknown to those skilled in the art. The density of the foam is suitablyabout 0.35 g/cm³ or less, or about 0.20 g/cm³ or less, or about 0.10g/cm³ or less, for example, about 0.02 to about 0.10 g/cm³. Foamexpansion ratio is generally about 10 or greater. Suitably, theabsorbent foam has about 5% or more closed cells, or about 10% or moreclosed cells, or about 15% or more closed cells to improve resiliencyand/or compression resistance.

The polymer melt can be continuously extruded to form a soft, flexible,open-cell, thermoplastic, absorbent foam. As explained above, theopen-cell content of the foam is controlled by adjusting the amounts ofplasticizing agent and surfactant. Open-cell content can be measuredusing a gas pycnometer according to ASTM D2856, Method C. The open-cellcontent of the resulting foam is suitably about 50% or greater, or about70% or greater, or about 80% or greater.

To produce thermoplastic foam, continuous plastic extrusion processesare typically utilized. (Certain injection molding and batch processescan also be employed.) Often tandem screw-type extruders are usedbecause of the need for tight control of extrusion temperatures toproduce open-cell foam. The first extruder typically contains severalzones including: feed and conveying, compression, melting, metering andmixing zones and if one extruder is being used, a cooling zone isutilized prior to polymer melt discharge, foaming, and shaping. Thefirst extruder is typically hopper loaded with resin and additives usingdry/blend/metering equipment and/or having the additive(s) incorporatedinto the pelletized polymer concentrate such as in a masterbatch. Theresins, additives, and/or masterbatch are then heated in the extruder toform a plasticized or melt polymer system, often with zoned temperaturecontrol using extruder cooling/heating systems. Physical blowing agentsare typically added after the melt temperature has been heated to atemperature at or above its glass transition temperature or meltingtemperature to form a foamable melt. The inlet for a physical blowingagent is typically between the metering and mixing zones. The blowingagent is mixed thoroughly with the melted polymer at a sufficientlyelevated pressure to prevent melt expansion. With a nucleating agent andblowing agent blended in the polymer melt, the foamable melt istypically cooled to a lower temperature to control the desired foam cellstructure. With tandem extruders, the cooling is done in a secondextruder which is connected downstream of the first extruder through aheated cross-over supply pipe. In single extruders, cooling is typicallydone upstream of the discharge orifice. Often cooling/heating systemswith process temperature control loops are incorporated to tightlycontrol foam bubble nucleation/growth within the melt. The optimumcooling temperature is typically at or slightly above the glasstransition temperature or melting point of the melt.

In one embodiment, a tandem extruder, such as illustrated in FIG. 21,can be utilized. This type of extruder 530 may be consideredparticularly suitable in some aspects because it has the ability toprovide tight control of extrusion temperatures to produce open-cellfoam. With tandem extruders 530, the first extruder section 532typically contains several zones including a feed zone 534, a conveyingzone 536, a compression zone 538, a melting zone 540, and a metering andmixing zone 542. The second extruder section 544 often contains acooling zone 546 and a shaping zone 548 prior to the discharge 550. Thefirst extruder 532 is typically hopper loaded with the base resin(s) aswell as any other desired additives, including thermoplastic elastomers,plasticizing agents, surfactants and/or fibers, for example. Techniquesknown in the art for accomplishing this include using dry blend/meteringequipment and/or having the components incorporated into a palletizedpolymer concentrate such as in a masterbatch. The components of the foamformula are then heated in the extruder 532 to form a plasticized ormelt polymer.

The foamable melt is then typically cooled to a lower temperature tocontrol the desired foam cell structure. In the case of tandem extruders530, the cooling is typically accomplished in the second extruder 544which is connected downstream of the first extruder 532 through a heatedcross-over supply pipe 552. In the case of single extruders (not shown),cooling is typically accomplished upstream of the discharge orifice.Often cooling/heating systems with process temperature control loops areincorporated to tightly control foam bubble nucleation/growth within thegas-laden melt. The optimum cooling temperature for foam formation istypically at or slightly above the glass transition temperature ormelting point of the melt.

The melt is then extruded through a die 554 to a lower pressure(typically atmospheric or a vacuum) and lower temperature (typicallyambient) environment to cause thermodynamic instability and foamingwhich then cools and crystallizes the plastic to form a stabilized foam556 which then solidifies to form a web or layer. Often circular,annular or slit dies, including curtain dies, and the like are used,often with a mandrel, to shape and draw the web to the desired gauge,shape, and orientation with foam expansion and cooling.

Various equipment configurations using such extrusion means can be usedto manufacture the foam composite of the present invention. In addition,various specialized equipment can be employed upstream of speciallydesigned dies to enhance mixing, cooling, cellular structure, metering,and foaming. Such equipment includes static mixers, gear pumps, andvarious extruder screw designs, for example. Stretching equipment,including roller nips, tenters, and belts, may also be used immediatelydownstream of the discharge to elongate cellular shape to enhanceabsorbency, for example. Microwave irradiation for cross-linking,foaming activation, and mechanical means can also be used to enhancefoam properties. Foam contouring, shaping (e.g., use of a wire meshpattern) and the like, using thermoforming, and other such thermalprocesses, including thermal bonding, can be used to control shaping,flexibility, softness, aesthetics, and absorbent swelling.

Both physical and chemical blowing agents, including both inorganic andorganic physical blowing agents, are used to create foaming. Suitableinorganic physical blowing agents include water, nitrogen, carbondioxide, air, argon, and helium. Organic blowing agents includehydrocarbons such as methane, ethane, propane, butanes, pentanes,hexanes, and the like. Aliphatic alcohols and halogenated hydrocarbons,including FREON® and HFC-134A, can also be used though in the latter,their use is generally avoided for environmental reasons. Endothermicand exothermic chemical blowing agents which are typically added at theextruder hopper include: azodicarbonamide, paratoluene sulfonylhydrazide, azodiisobutyro-nitrile, benzene sulfonyl hydrazide, P-toluenesulfonyl hydrazide, barium azodicarboxylate, sodium bicarbonate, sodiumcarbonate, ammonium carbonate, citric acid, toluene solfonylsemicarbazide, dinitroso-pentamethylene-tetramine, phenyltetrazolesodium borohydride, and the like. Mixtures and combinations of variousphysical and chemical blowing agents can be used and often are used tocontrol cell structure. Blowing agent activators can be added to lowerthe decomposition temperature/profile of such chemical blowing agents.Such activators include metals in the form of salts, oxides, ororganometallic complexes.

Open-cell formation can be regulated by elevated processing pressuresand/or temperatures and use of nucleating agents and chemical blowingagents which can control both cell density and cell structure. Variousbase resins are sometimes used to broaden the foaming temperature tomake open-cell foam. Open-cell level can be facilitated by adding smallamounts of various immiscible polymers to the foam polymer formula suchas adding polyethylene or ethylene/vinyl acetate copolymer topolystyrenic-based foam systems to create interphase domains that causecell wall rupture. By regulating the polymer system components andcrystallization initiating temperature, open-cell content andmicroporous cell membrane uniformity can be controlled. Ethylene-styreneinterpolymers can be added to alkenyl aromatic polymers to controlopen-cell quality and improve surface quality and processability. Smallamounts of polystyrene-based polymers are sometimes added topolyolefin-based foams to increase open-cell content.

Additives, such as nucleating agents, can also be employed to obtaindesired fine open-cell structure. The amount of nucleating agent willvary according to the cell structure desired, foaming temperature,pressure, polymer composition, and type of nucleating agent utilized.Typically with increasing nucleating agent, cell density and open-cellcontent increase. Nucleating agents include calcium carbonate, blends ofcitric acid and sodium bicarbonate, coated citric acid/sodiumbicarbonate particles, nanoclays, silica, barium stearate, diatomaceousearth, titanium dioxide, talc, pulverized wood, clay, and calciumstearate. Stearic acid, salicylic acid, fatty acids, and metal oxidescan also be used as foaming aids. Other thermoplastic polymers can alsobe used for such purposes. These are typically dry blended or added withthe polymer concentrate.

Various additives such as lubricants, acid scavengers, stabilizers,colorants, adhesive promoters, fillers, smart-chemicals, foamregulators, various UV/infrared radiation stabilizing agents,antioxidants, flame retardants, smoke suppressants, anti-shrinkingagents, thermal stabilizers, rubbers (including thermosets),anti-statics, permeability modifiers, and other processing and extrusionaids including mold release agents, and anti-blocking agents, and thelike can also be added to the foam polymer formula.

Secondary, or post-treatment, processes can be performed to improve,among other things, absorbency, cellular orientation, aesthetics,softness, and similar properties. This can be accomplished throughnumerous techniques known in the art including mechanical needling andother mechanical perforation (such as to soften foam and increaseopen-cell content), stretching and drawing (such as for cellularorientation and softening), calendering or creping (such as to softenand rupture cell membranes to improve cellular intercommunication),brushing, scarfing, buffing/sanding, and thermoforming (such as to shapethe foam composite). Often a foam surface skin may form duringextrusion, which can later be skived or sliced off, needle-punched,brushed, scraped, buffed, scarved, sanded, or perforated to remove thebarrier. Depending on the specific usage of the foam, application of asurfactant after the foaming process or needling process may further beutilized to afford a desired wettability.

FIG. 22 illustrates one exemplary process for hydraulically needling athermoplastic foam layer. In this example, a foam layer 682 is supportedon an apertured foraminous support or carrier belt 684 of a hydraulicneedling machine 690. The carrier belt 684 is supported on two or morerolls 686A and 686B provided with suitable driving means (not shown) formoving the belt 684 forward continuously. The carrier belt 684 may, forexample, be a single plain weave foraminous wire having a mesh size fromabout 20 to about 150. Alternatively, a perforated plate (not shown) canbe utilized as a backing carrier.

The foam layer 682 is then passed under one or more manifolds 692. Thehydraulic needling process may be carried out with any appropriateworking fluid such as, for example, water. The working fluid isgenerally evenly distributed by the manifold 692 through a series ofindividual holes or orifices 694 which may be from about 0.003 to about0.015 inch (0.076 to 0.381 mm) in diameter. In some aspects, the workingfluid passes through the orifices 694 at a pressure generally rangingfrom about 50 to about 3000 pounds per square inch gage (psig) (344 to20685 KPa), such as about 60 to about 1500 psig (414 to 10342 KPa) orabout 100 to about 800 psig (686 to 5516 KPa), or even about 200 toabout 600 psig (1379 to 4137 KPa). In general, thermoplastic foam layersmay utilize a fluid pressure ranging from about 60 to about 400 psig(414 to 2758 KPa), when one to four manifolds are used. However, greaterneedling energy may also be desired or required for high basis weightmaterials, stiffer modulus, higher line speeds, and the like.

Water jet treatment equipment and other hydraulic needling equipment andprocesses which may be adapted can be found, for example, in U.S. Pat.No. 3,485,706 to Evans, and in an article by Honeycomb Systems, Inc.entitled “Rotary Hydraulic Entanglement of Nonwovens,” reprinted fromINSIGHT 86 INTERNATIONAL ADVANCED FORMING/BONDING CONFERENCE, both ofwhich are incorporated herein by reference in a manner consistentherewith. In some aspects, the invention may be practiced using amanifold containing a strip having 0.007 inch diameter orifices, 30orifices per inch and one row of orifices such as that produced by MetsoPaper USA, Inc., a business having offices located in Biddeford, Me.,U.S.A. Other manifold configurations and combinations such as thoseavailable from Fleissner GmbH, a business having offices in Egelsbach,Germany or Rieter Perfojet S.A., a business having offices located inWinterthur, Switzerland, may also be used. For instance, in some aspectsa single manifold may be utilized, whereas in other aspects severalmanifolds may be arranged in succession.

The resulting columnar jetted streams 696 of the working fluid impact onthe foam layer 682, thereby puncturing the skin which may have formed onthe foam layer surface during formation, and increasing the open-cellcontent of the layer. Additionally, vacuum slots in a suction box(es)695 may be located directly beneath the hydraulic needling manifold(s)694 and beneath the carrier belt 684 as well as downstream of theneedling manifold(s) 694 to remove excess water from the hydraulicallyjet-treated material 698. The hydraulically jet-treated foam layer 698can then be dried using means known in the art.

Calendaring and creping can also be used to soften and rupture cellmembranes to improve cellular connectivity, and thermoforming can beused to shape the foam absorbent. Mechanical, hydraulic, thermal, orlaser perforation can also be used to soften foam and further increaseopen-cell content.

Post-densification of the foam structure, after extrusion, can beemployed to enhance functionality. The foam of the invention can belaminated to other layers, resulting in structures having variousfunctionalities.

EXAMPLES Example 1

Foam polymer formulas were made from blends of Dow STYRON® 685Dpolystyrene pelletized resin and KRATON® G1657styrene-ethylene-butylene-styrene (SEBS) block copolymer pelletizedthermoplastic elastomer resin. Low molecular weight polyethylene wax(Eastman EPOLENE® C-10) was added to certain samples to plasticize thefoam polymer formula. A surfactant, Dow-Corning 193, available fromDow-Corning Company in Midland, Mich., U.S.A., was added to certainsamples to improve wettability. A nucleating agent, CLOISITE® 20A, wasalso added at 5%, by weight, to the foam polymer formula. All foams wereextruded using a 27-mm Leistritz co-rotating twin screw extruder,available from American Leistritz Extruder Corporation in Somerville,N.J., U.S.A., equipped for direct injection of carbon dioxide gas. Thefoam polymer formulas were heated to about 200 degrees Celsius in theextruder and subsequently foamed using carbon dioxide (added at 6%, byweight, of the foam polymer formula) as a blowing agent. Extrusiontemperatures and pressures were adjusted for optimum foam expansion andopen-cell connectivity. Table 1 shows the foam polymer formula for eachof the six samples formed. Amounts are recorded in terms of percentageby weight of the foam polymer formula, with the foam polymer formulaincluding: polystyrene, SEBS, nucleating agent, and, when present,surfactant/polyethylene wax. TABLE 1 Foam Polymer Formulas SamplePolystyrene SEBS PE Wax Surfactant 1a 47.5% 47.5%   0%   0% 2a 47.5%42.7%   0% 4.8% 3a 47.5% 38.4% 4.3% 4.8% 4a 47.5% 25.6% 17.1%  4.8% 5a79.3% 8.5% 5.6% 1.6% 6a 47.5% 37.1% 5.6% 4.8%

Each of the samples was tested to determine foam density, apparentopen-cell content, compression modulus, resiliency, and strain. Table 2shows a comparison of these foam properties for each of the samples.Also included in Table 2 for comparison purposes is RYNEL® 562-B, acommercially available absorbent foam from Rynel Ltd. Co. in Boothbay,Me., U.S.A. More particularly, 562-B is a medical-grade hydrophilicpolyurethane foam. Though expensive for many disposable productapplications and not readily process recyclable, such thermoset foam hasbeen demonstrated to have functional absorbency, mechanical andaesthetic properties for personal care and medical foam applications.

Foam density was calculated using the basis weight measurement asdescribed in ASTM D1622-98, and the bulk was measured using a handmicrometer and surface compression was avoided. Open-cell content wasmeasured by a gas pycnometer using ASTM D2856, Method C. Compressionmodulus, resiliency, and strain were each measured using ASTM D3575.Modifications were made to the ASTM methods to accommodate samplegeometries. The modifications were not made to change the outcome of thetest. TABLE 2 Foam Properties Strain Foam Open- Compression (%) at 1 psiDensity, Cell Modulus, Resil- (6.8 KPa) lb/ft³ Content psi iency ofSample (g/cm³) (%) (KPa) (%) pressure 1a 21 (0.34) 58 128 (883)  — 1.42a  7 (0.11) 86 21 (145) 98 6.2 3a  6 (0.10) 89 22 (152) 98 8.7 4a 20(0.32) 67 6 (41) — 36.7 5a 55 (0.88) 21 — — — 6a  7 (0.11) 85 3 (21) 9936.3 RYNEL ®  6 (0.10) 92 4.6 (32)   99-100 26.8 562-B

As shown in Table 2, the foam polymer formula without either aplasticizing agent or surfactant has a high density (Sample 1a). Sample2a illustrates the substantial lowering of density through addition ofsurfactant alone. Sample 3a illustrates that density can be lowered evenmore and open-cell content can be raised through a combination ofsurfactant and plasticizing agent. Samples 4a and 5a illustrate thedetrimental effect of an excessive amount of plasticizing agent withrespect to the amount of surfactant.

Samples 5a and 6a, together, illustrate that foam expansion with higherlevels of wax can be improved by increasing the level of the surfactant.With respect to Sample 5a, at a 1.6% surfactant loading, the foamdensity is 55 lb/ft³ (0.88 g/cm³) which is nearly that of the rawunmodified polystyrene (65 lb/ft³ or 1.04 g/cm³), while with Sample 6aat a 4.8% surfactant loading (and with further addition of KRATON G1657,which is more difficult to foam than polystyrene), the foam densitydecreases to about 7 lb/ft³ (0.11 g/cm³). Open-cell contents weremeasured at greater than 80% under such conditions.

Photomicrographs of Samples 2a, 3a, and 4a are provided in FIGS. 1-3,respectively. A photomicrograph of RYNEL® 562-B foam is shown in FIG.17.

FIG. 1 shows the foam polymer formula without wax addition. The straightcellular walls indicate full cellular expansion with possible continuedexpansion while the foam polymer formula was cooling.

FIG. 2 shows the impact of adding 4.3% wax. The cell walls arecorrugated. Gas was lost from the cells (possibly due to cell wallopenings) and cells began to collapse after the cell walls weresolidifying, but still soft. The result is the corrugated look of thecell walls.

FIG. 3 shows the impact of adding 17.1% wax. There are large areas thatare not foamed. This is due to full collapse of the cells from too muchplasticization.

Example 2

This example illustrates the importance of surfactant structure toenable the production of low-density foams from a blend of polystyrenewith soft, flexible polymers. The foam polymer formula in this exampleincluded 50.0 parts of Dow STYRON® 685D polystyrene and 45.2 parts ofKRATON® G1657 SEBS, and 4.8 parts CLOISITE 20A nanoclay. Foam extrusionmethod was the same as Example 1. Samples of the foam polymer formulawith various surfactants, and levels of surfactant, and results of thesesamples are shown in Table 3. TABLE 3 Foaming Soft, Flexible PolymersWith Various Surfactants Surfactant Amount (parts per 100 parts FoamOpen- of foam Density, Liquid Cell polymer lb/ft³ Penetration ContentSample Surfactant Description formula) (g/cm³) into Foam (%) 1b NoSurfactant 0 57 (0.91) No 24 2b Clariant HOSTASTAT 2.7  7 (0.11) Yes 84HS-1 (sulfuric acid head C12-C18 saturated tail) 3b Dow Corning 193 4.613 (0.21) Yes 76 (ethoxylated silicone polymer) 4b Cognis EMEREST 26502.7 10 (0.16) No 82 (PEG 400 head C12 saturated tail) 5b Cognis EMEREST2648 2.7 13 (0.21) No 57 (PEG 400 head C18 unsaturated tail) 6b CognisEMEREST 2712 2.7 11 (0.18) No 60 (PEG 400 head C18 saturated tail)

The results in Table 3 illustrate the impact of surfactant selection onfoam density and wettability. Wettability is indicated by thepenetration of five water droplets into the 5 mm thick foam through ade-skinned portion of the foam.

Sample 1b, the only sample without a surfactant, has a much higherdensity and a considerably lower open-cell content than each of thesamples that includes a surfactant. There was no liquid penetration intothe foam. Foams produced with HOSTASTAT HS-1 having a sulfuric acid head(Sample 2b) and Dow Corning's ethoxylated silicon surfactant (Sample 3b)had liquid penetration while the Cognis surfactants with a PEG 400 head(Samples 4b-6b) had no liquid penetration, even with comparableopen-cell content (Sample 4b vs. Samples 2b and 3b).

Example 3

This example illustrates the effect of multiple surfactants incomparison to single surfactants in the foam polymer formula. Table 4illustrates the results of adding various dosages of surfactants andsurfactant mixtures to a polymer blend of 54.45 parts of Dow STYRON®685D polystyrene, 44.55 parts of KRATON® G1657 with 1 part of MISTRON®VAPOR talc, used as a nucleant, and available from Luzenac America,Inc., of Englewood, Colo., U.S.A. The surfactants utilized were:HOSTASTAT® HS-1, an alkyl sulfonate available from Clariant Corporationin Winchester, Va., U.S.A.; MMF 184 SW, an ethoxylated siloxaneavailable from Siltech LLC in Dacula, Ga., U.S.A.; and MASIL® SF-19, anethoxylated siloxane available from BASF Corporation in Mount Olive,N.J., U.S.A. Foam extrusion method was the same as Example 1 except thatthe maximum extrusion temperature utilized was 195 degrees Celsius andcarbon dioxide addition rate was about 15%, by weight of the foampolymer.

In Table 4, the foam saline intake rate is quantified by taking twelvesections of foam, each with a cleanly cut surface, and placing a drop of0.9% NaCl saline solution on each surface. If the drop was absorbedrapidly enough that no meniscus was formed by the drop, that section wasrated as 9. If the droplet was absorbed in one second or less but didform a meniscus, then the section was rated 5. If the droplet wasabsorbed between one second and ten seconds, the section was rated 3. Ifthe droplet was not absorbed within ten seconds, then the section wasrated 0. The average of the twelve sections tested is presented in Table4. TABLE 4 Comparison of Single-Surfactant and Multi-Surfactant SystemsDosage (surfactant Foam parts per 100 Foam Saline parts of foam Density,Intake polymer lb/ft³ Rating Sample Surfactant formula) (g/cm³) (0-9) 1cHOSTASTAT HS-1 3 11 (0.18) 8.7 2c HOSTASTAT HS-1 1 21 (0.34) 3.8 3cMMF184SW 3 18 (0.29) 3.3 4c MMF184SW 1 23 (0.37) 2.5 5c MASIL SF-19 3 20(0.32) 7.7 6c MASIL SF-19 1 22 (0.35) 0.0 7c 3 parts MASIL SF-19 + 1 112 (0.19) 5.7 part HOSTASTAT HS-1 8c 4 parts MASIL SF-19 + 1 0.5 12(0.19) 0.0 part HOSTASTAT HS-1 9c 3 parts MMF184SW + 1 1 11 (0.18) 0.0part HOSTASTAT HS-1 10c  4 parts MMF184SW + 1 0.5 13 (0.21) 7.3 partHOSTASTAT HS-1 11c  None 0 30 (0.48) 0.0

The results from Table 4 show that a mixture of the surfactants in thefoam polymer formula at a dosage of 1 part surfactant per 100 parts offoam polymer formula produces foam with lower density than produced with1 part surfactant per 100 parts of foam polymer formula of any of thesingle surfactants. Even at dosages of 0.5 parts of surfactant per 100parts of foam polymer formula, the two-surfactant system showed synergyin producing lower density foam. The two-surfactant foams had densitiescomparable to foam made with over three times the amount of thebest-performing single-surfactant system. The saline intake was somewhatreduced with the two-surfactant system; however, spontaneous fluidintake was still possible with low dosages of specific two-surfactantsystems as measured by a saline intake rating of greater than 5 forSamples 7c and 10c.

Photomicrographs of some of the foam samples in Table 4 are presented inFIGS. 4-12. These figures further emphasize the synergy of themulti-surfactant system for foam extrusion. All photomicrographs are ata 20× magnification. The surface of the foam was stained red to aid invisual observation of the cell structure. These figures show therelative uniform cell structure provided by the multi-surfactant system.

Example 4

This example illustrates the effect of diblock copolymer content on theflexibility and absorbent properties of foams containing a thermoplasticelastomer (TPE).

Table 5 contains published information on the molecular properties ofKRATON® thermoplastic elastomers used in this example. KRATON®thermoplastic elastomers are available from Kraton Polymers of Belpre,Ohio, U.S.A. TABLE 5 Properties of KRATON ® Thermoplastic ElastomersPolystyrene Content Diblock Content Molecular Polymer (%) (%) WeightKRATON ® D1111 22% 15% KRATON ® D1119 22% 66% KRATON ® D1160 18.5%  168000-188000 KRATON ® D1161 15% 207000-237000

Various amounts of KRATON® D1111 and KRATON® D1119 were added to a blendof Dow STYRON® 685D polystyrene, Clariant HOSTASTAT® HS-1 antistaticagent, Ciba IRGAFOS® 168, a phosphate stabilizer that acts as asecondary antioxidant, available from Ciba Specialty Chemicals, Inc.,Tarrytown, N.Y., U.S.A., and Luzenac MISTRON® Vapor Talc. These wereadded so that the composition was 62.5 parts of Dow STYRON® 685D, 33.6parts of KRATON® polymer(s), 2.8 parts of Clariant HOSTASTAT® HS-1, 0.9parts of Luzenac MISTRON® Vapor Talc and 0.2 parts of Ciba IRGAFOS® 168.Table 6, from published Kraton literature, describes the amount of eachKRATON® polymer added in each sample and the effective amount of diblockcopolymer. Foam extrusion method was the same as Example 1 except thatthe maximum extrusion temperature utilized was 195 degrees Celsius andcarbon dioxide addition rate was between 12% and 14%, by weight. TABLE 6Diblock Content of Samples Containing KRATON ® Thermoplastic ElastomersDiblock Content Sample KRATON ® D1111 KRATON ® D1119 (%) 1d 100 0 15% 2d66 34 32% 3d 0 100 66%

Foam Samples 1d-3d were extruded using a 27-mm Leistritz co-rotatingtwin screw extruder equipped for direct injection of carbon dioxide gas.The carbon dioxide was injected at a rate of 10-12 ml./min. and polymerwas extruded at a rate of 4.5 lbs./hr (2.04 kg/hr). Extrusiontemperatures and pressures were adjusted to obtain maximum foamexpansion. Properties of the foam are presented in Table 7. Thecompression modulus and bending pressure were measured by compression ofthe foam sample between two plates. The foam sample, one inch (2.54 cm)in length by less than 0.4 inch (1.02 cm) in diameter, was placed withthe long dimension positioned perpendicular to the compression plates.The plates were compressed at a constant rate of 5 cm/min. and the forceto achieve this rate was recorded. The force was normalized using thecross-sectional area of the sample in contact with the compressingplates, yielding units of pressure. The pressure required to bend thesample, which appeared as the maximum pressure, was the bendingpressure. The modulus Was identified as the slope of the pressure in thelimit of zero strain (approaching no compression of the sample).

Open-cell content was measured using a gas pycnometer utilizing ASTMD2856 method C. Foam saline fluid intake rating was measured by thefollowing method: a specimen is cut to a 0.25 inch (0.64 cm) width (foamoriented MD) and placed so that a cut edge is perpendicular to gravity.One droplet of 0.9% NaCl saline solution is placed onto the specimen. Ifthe droplet is immediately absorbed, the intake rating of 9 is given tothe specimen. If the droplet is absorbed within a second but is slowenough that a meniscus is formed on the surface, the intake rating forthe specimen is assigned a value of 5. If the droplet is absorbed withinfive seconds, the fluid intake rating of the specimen is 3. If asubstantial amount of fluid is absorbed into the foam but the droplet isnot completely absorbed within five seconds, the specimen intake ratingis assigned a value of 1. The specimen intake rating is zero if littleor none of the droplet is absorbed by the foam within five seconds. Thereported rating is the average of at least twelve tested specimens. Afluid intake rating of 5 or greater is desirable for use in high-flowabsorbent applications such as diapers. TABLE 7 Properties of FoamsHaving Various Diblock Content Foam fluid Foam Saline Density,Compression Bending Open-Cell Intake lb/ft³ Modulus, Pressure, ContentRating Sample (g/cm³) psi (KPa) psi (KPa) (%) (0-9) 1d 11 (0.18)  2880(19858) 166 (1145) 69% 8.7 2d 9 (0.14) 740 (5102) 132 (910)  69% 7.0 3d6 (0.10) 259 (1786) 30 (207) 69% 9.0

As can be seen from Samples 1d, 2d, and 3d, increasing the amount ofdiblock copolymer in the thermoplastic elastomer reduces the foamdensity and decreases the foam stiffness as measured by modulus andbending pressure. The increase of diblock content in the thermoplasticelastomer did not impact the open-cell content and all samples had highfluid intake ratings.

Table 8 displays the absorbent properties of foam Sample 3d of theinvention compared to commercially available foams. RYNEL® 562-B is asoft, flexible, medical-grade hydrophilic polyurethane foam, availablefrom Rynel Ltd. Co. in Boothbay, Me., U.S.A. Absorbent polystyrene-basedopen-cell rigid meat-tray foam from Genpak LCC: Food Service Division inGlens Falls, N.Y., U.S.A., is also provided for comparison. FIG. 18 is aphotomicrograph of the GENPAK® foam. The absorbent properties displayedby the foam of the invention are similar to many of the absorbentproperties of the commercially available RYNEL® foam. However, the foamof the invention is advantageous in that it is thermoplastic foam and istherefore recyclable, unlike thermoset foams such as Rynel foam. TheGENPAK® polystyrene foam is not as absorbent and is not soft, flexible,and resilient as is the foam of the invention.

More particularly, the absorbent capacity of the tabled foam samples wastested using 0.9% NaCl solution in accordance with the SaturatedCapacity Test Method, described herein. The viscous fluid capacity wastested according to the Saturation Capacity and Retention Capacity TestMethod, described herein, using menses simulant. The Fluid Intake Fluxof each foam sample was tested using 0.9% NaCl solution in accordancewith the Fluid Intake Flux Test Method (Rynel and Genpak® foams) orModified Fluid Intake Flux Test (Sample 3d), described herein.Additionally, the vertical capillarity of each foam sample was testedusing 0.9% NaCl solution, in accordance with the Vertical Wicking TestMethod, described herein. TABLE 8 Absorbent Properties of Foams 0.9%NaCl Saturated Capacity (g/g) and Fluid Intake Flux Viscous Fluid 0.9%NaCl Saturation 3 Insults Capacity/Retention ml/sec/in² VerticalCapacity (g/g) (m1/sec/cm²) Wicking in Menses 1^(st) 2^(nd) 3^(rd) 30mins. (cm) Sample 0.9% NaCl Simulant Insult Insult Insult 0.9% NaCl 3d4.0 4.9/2.3 6.5 (1.0)  2.4 (0.37) 1.9 (0.29) 7.6 RYNEL ® 562-B 9.016.4/3.5  2.7 (0.42) 2.0 (0.31) 1.9 (0.29) 7.0 GENPAK ® PS 2.2 0.2(0.03) 0.1 (0.02) 0.1 (0.02) 3.9 absorbent meat tray

Additionally, Samples 2b (Example 2) and 3d (Example 4) were tested forsurfactant permanence in accordance with the Surfactant Permanence Test,described herein. It was found that Sample 2b had 0.00045 g ofsurfactant dissolved from a total possible of 0.0325 g, which is 1.39%dissolved and 98.61% remaining in the foam after a 24-hour soak. Sample3d had 0.000288 g of surfactant dissolved from a total possible of 0.018g, which is 1.6% dissolved and 98.4% remaining in the foam after a24-hour soak.

Example 5

This example illustrates the effect of thermoplastic elastomer molecularweight on the flexibility and absorbent properties of foams.

KRATON® D1160 and KRATON® D1161 were each added to a blend of DowSTYRON® 685D polystyrene, Clariant HOSTASTAT® HS-1 antistatic agent,Ciba IRGAFOS® 168 and Luzenac MISTRON® Vapor Talc. These were added sothat the composition was 62.5 parts of Dow STYRON® 685D, 33.6 parts ofKRATON® polymer, 2.8 parts of Clariant HOSTASTAT® HS-1, 0.9 parts ofLuzenac MISTRON® Vapor Talc, and 0.2 parts of Ciba IRGAFOS® 168. Thiswas done to discern the impact of thermoplastic elastomer molecularweight on foam properties, which are given in Table 9. The sample foamswere extruded in a 27 mm Leistritz co-rotating twin screw extruderequipped for direct injection of carbon dioxide gas. The carbon dioxidewas injected at a 6-12% loading, by weight, and polymer was extruded ata rate of 4.5 lb/hr (2.04 kg/hr). Extrusion temperatures and pressureswere adjusted to obtain maximum foam expansion. The increased molecularweight of KRATON® D1161 (Sample 2e) compared to KRATON® D1160 (Sample1e) provided for a foam of a lower density. The reduced modulus andbending pressure of Sample 2e compared to Sample 1e is due to thecombination of the increased molecular weight and decreased polystyrenecontent of KRATON® D1161 compared to KRATON® D1160. In addition, it wasqualitatively observed that with TPE included in the foam polymerformula in the foam samples, the foam was elastic and resilient in theX, Y and Z planar dimensions. This was seen by the stretch, recovery,and compression resiliency properties of the invention foams. Thedifferences between these two thermoplastic elastomers also amounted todifferences in the open-cell content and 0.9% NaCl saline Fluid IntakeRating. TABLE 9 Foam Properties of Foams Having Different MolecularWeight TPE Foam Bending Open- Density, Compression Pressure, Cell FluidIntake KRATON ® lb/ft³ Modulus, psi psi Content Rating Sample Polymer(g/cm³) (KPa) (KPa) (%) (0-9) 1e D1160 20 (0.32) 8185 (56440) >244(>1680) 56% 5.0 2e D1161 16 (0.26) 887 (6120) 62 (430) 64% 8.0

Based on these results, it is desirable to utilize a thermoplasticelastomer with high diblock content and high molecular weight as part ofthe foam polymer formula to extrude low-density, soft, flexible,resilient, elastic, absorbent, thermoplastic foam.

Example 6

This example shows the production of foam using thermoplastic elastomeras the plasticizing agent, yielding unique properties achieved with theinvention including absorbent capacity, bending modulus and low density.The foam layer was formed using a 2.5/3.5 inch (6.35/8.89 cm) tandemextrusion system and annular die similar to that described in U.S. Pat.No. 6,273,697 to Harfmann and U.S. Pat. No. 6,638,985 to Gehlsen (whichare incorporated herein by reference in a manner that is consistentherewith), or equivalents. The primary extruder temperature and screwspeed were adjusted to ensure complete polymer and additives melting andmixing and the secondary extruder temperature was adjusted to achievethe desired melt temperature profile to produce foam. The die pressurewas achieved by controlling the die gap and extruder screw speeds. Theextruded foam was pulled over a cooling mandrel, slit, and wound in aroll.

The thermoplastic foam used polystyrene (STYRON 685D from Dow ChemicalCompany), thermoplastic elastomer (KRATON DHV, astyrene-ethylene-butylene-styrene block copolymer, from KratonPolymers), surfactant (CESA-STAT® 3301 from Clariant Corp.) and nucleant(HYDROCEROL® CF-40 T from Clariant Corp. and talc: A27678 fromPlastimerics Inc.).

In this example isopentane and carbon dioxide were combined as aphysical blowing agent and HYDROCEROL® CF-40-T was used as a chemicalblowing agent/nucleant. The raw materials and process parameters used inExample 6 are shown in Table 10. TABLE 10 Raw Material and ProcessParameters Sample Sample Process Conditions Units 1f 2f Polystyrene (DowSTYRON ® 685D) weight % 47.1 45.1 Thermoplastic Elastomer (KRATON DHV)weight % 40 49 HYDROCEROL ® (Clariant) weight % 7.5 0 CESA-STAT ® 3301(Clariant) weight % 5.4 5.4 Talc A27678 (Plastimerics Inc.) weight % 00.5 Physical blowing agent - iso-pentane wt. % of polymer 5.5 3.9Physical blowing agent - carbon dioxide wt. % of polymer 0 2.2 Primaryextruder speed Rpm 100 100 Secondary extruder speed Rpm 12 12 Primaryextruder last zone temp F. (C.) 410 (210) 410 (210) Secondary extruderlast zone temp F. (C.) 254 (123) 241 (116) Die body temperature F. (C.)295 (146) 295 (146) Melt temperature F. (C.) 285 (141) 280 (138) Diepressure psi (Kpa) 931 (6419) 1497 10322) Pull roll speed fpm (m/min) 45(13.7) 45 (13.7) Foam throughput (calculated) lb/hr (kg/hr) 165 (75) 178(81)

The resulting foam sheet was hydraulically post treated by cutting thesheet into smaller hand samples, placing the sheets on a moving wire andsending the sheets under water jets used to compromise the surface ofthe foam to improve among other things, absorbency, cellularorientation, aesthetics, softness, and similar properties. The handsamples were hydraulically treated using a Honeycomb Systems manifold(available from Honeycomb Systems Inc., a business having officeslocated in Biddeford, Me., U.S.A.), having a jet strip with 0.005 inch(0.127 mm) diameter orifices, 40 orifices per linear inch (16 orificesper cm) arranged in a single row (available from Nippon Nozzle, abusiness having offices located in Kobe, Japan). Each hand sample waspassed under the manifold four times, twice per side, at a line wirespeed of 25 feet (7.62 meters) per minute and the dewatering vacuumlevel under the manifold was adjusted to 20 inches (508 mm) of Hg toensure adequate dewatering. The pressure of the water jets was adjustedto 1000 psig (6895 KPa) to adequately open the skin of the foam to makeit liquid permeable. Each foam layer was then dewatered using the wirevacuum and was air dried overnight.

The foams were tested in comparison to a polyurethane foam, RYNEL® 562-Bdescribed earlier, and an airlaid sample. The airlaid sample wasproduced on a DanWeb line using 90% untreated pulp (non-debonded NB-614from Weyerhauser Corp.) and 10% binder fiber (T255 from Kosa Inc.). Theresults of this testing are shown on table 11 and table 12. TABLE 11Foam Attributes and Fluid Properties Saturated Vertical Capacity Intakeflux Wicking # of sides Basis 0.9% Functional 0.9% NaCL flux @ postWeight Density Open NaCL Capacity 1^(st) Insult 0 height Sample treatedgsm g/cc cell % g/g g/cc ml/sec/cm² g/sec/m² 1f 0 140.5 0.054 92 1.30.08 1.2 1f 1 127.4 0.057 92 4.6 0.30 0.098 5.4 1f 2 121.9 0.057 94 6.90.45 0.059 8.9 2f 0 119.2 0.038 90 0.7 0.03 0.8 2f 1 119.2 0.039 92 5.70.25 0.105 4.3 2f 2 117.8 0.040 92 9.1 0.41 0.233 5.9 RYNEL n/a 171.50.110 93 10.0 1.33* 0.244 −0.4 562-B Airlaid n/a 176.0 0.085 9.5 0.900.397 2.1*The RYNEL 562-B foam swells when wet and therefore has a higher actualcapacity than the theoretical capacity measured dry.

TABLE 12 Foam Mechanical Properties Dry Bending Edge Tensile Wet TensileStatic # of Modulus Compression Compression Peak load Peak load % WetTrap Tear Coefficient sides post MD/CD Resistance Peak load MD/CD MD/CDtensile loss Avg. peak of Friction Sample processed KPa @ 1 mm % SetMD/CD g kg kg MD/CD % MD/CD g side 1/side 2 1f 0 44137/2572  7 1315/233610.16/5.22  10.07/5.35  <1/<1 635/227 0.53/0.36 1f 1 1379/738  7 1f 2441/407 5  476/1019 9.21/2.86 8.48/2.72 7.9/4.9 862/209 0.60/0.50 2f 01158/490  14  926/1418 10.98/5.08  11.29/5.08  <1/<1 513/259 0.83/0.542f 1 510/193 11 539/902 9.16/3.45 9.48/3.36  <1/2.6 612/213 0.82/0.71 2f2 496/197 8 341/644 8.16/2.13 8.12/2.18 <1/<1 880/154 0.92/0.73 RYNELn/a 2910/1965 4 46/61 3.76/2.77 1.59/1.59 57.7/42.6 771/503 1.55 562-BAirlaid n/a 7067/4461 19 797 4.76 2.90 39.1 445 0.44

TEST METHODS Bending Modulus Test

This test is similar to that described in ASTM D 5934. Samples are cutto have dimensions of 64 mm long×38 mm wide (W). The thickness of thesample (T) is then measured in millimeters. With reference to FIGS. 20Aand 20B, assemble the apparatus 460 so that the balance 462 iscompletely on the baseboard 464, and the loading nose 466 is centeredover the weigh pan 468. The fixture base 470 should be inspected to besure that the distance between the centers 472, 474 of the two cylinders476, 478 (S) is 40 mm. The fixture base 470 should be placed on theweigh pan 468 so that the two cylinders 476, 478 are parallel with thecylinder on the loading nose 466. The caliper 482 should be adjusted tolower the assembly 480 with the loading nose 466 in order to be surethat the loading nose 466 is parallel to the bottom cylinders 476, 478.The sample (not shown) should then be laid across the bottom cylinders476, 478 with the longer dimension along the span. The loading nose 466should not touch the sample. At this point, the balance 462 should betared.

Dial the caliper 482 to move assembly 480 down so that the loading nose466 just touches the sample and the balance 462 reading (load) is 0.5 g.Then zero the caliper 482; this will be the reference point fordeflection measurements. Set a timer (not shown) for 2 minutes. Dial thecaliper 482 to move the loading nose 466 down to 1.0 mm distance (D)then start the timer. Record the load (F) in grams after 2 minutes, thendiscard the sample. The Bending Modulus (BM) at 1.0 mm deflection can becalculated in g/mm² using the following formula:${BM} = \frac{F\left( S^{3} \right)}{4{D\left( T^{3} \right)}W}$

To convert the BM to KPa, multiply the above result by 9.8.

Static Coefficient of Friction Test

Coefficient of friction was tested in accordance with ASTM D1894 using aSintech 2/S test apparatus from MTS. The apparatus is set up as in FIG.1 method C in ASTM D1894. Sample size is 2.5×7 inches (6.35×17.8 cm) andwrapped around the sled so that the tested side is facing out and incontact with the test surface. Glass was used as the test surface. Thestatic coefficient of friction was calculated and an average of fivesamples was reported.

Dry and Wet Tensile Strength, West Tensile Loss

Dry and Wet tensile strength testing was conducted using the cut striptest method at constant rate of extension in accordance with ASTM D5035.The sample size was modified from the ASTM method and was equal to 3×6inches (7.62×15.2 cm). The wet strength was carried out as specified inthe ASTM method. No surfactant was added to the water during thetesting. Percent wet tensile loss is the percent of tensile loss due towetting the material. Percent wet tensile loss is calculated with thefollowing formula:% Wet Tensile Loss=(Dry Tensile−Wet Tensile)/Dry Tensile*100.

Foam Caliper (Bulk) Test Method

The caliper or thickness of a material, in millimeters, is measured at0.05 PSI (0.345 KPa) using a Frazier spring model compresometer #326bulk tester with a 2 inch (50.8 mm) foot (Frazier Precision InstrumentCorporation, 925 Sweeney Drive, Hagerstown, Md. 21740). Each type ofsample is subjected to three repetitions of testing and the results areaveraged to produce a single value.

Saturated Capacity Test Method

Saturated Capacity is determined using a Saturated Capacity (SAT CAP)tester with a Magnahelic vacuum gage and a latex dam, comparable to thefollowing description. Referring to FIGS. 13-15, a Saturated Capacitytester vacuum apparatus 110 comprises a vacuum chamber 112 supported onfour leg members 114. The vacuum chamber 112 includes a front wallmember 116, a rear wall member 118 and two side walls 120 and 121. Thewall members are sufficiently thick to withstand the anticipated vacuumpressures, and are constructed and arranged to provide a chamber havingoutside dimensions measuring 23.5 inches (59.7 cm) in length, 14 inches(35.6 cm) in width and 8 inches (20.3 cm) in depth.

A vacuum pump (not shown) operably connects with the vacuum chamber 112through an appropriate vacuum line conduit and a vacuum valve 124. Inaddition, a suitable air bleed line connects into the vacuum chamber 112through an air bleed valve 126. A hanger assembly 128 is suitablymounted on the rear wall 118 and is configured with S-curved ends toprovide a convenient resting place for supporting a latex dam sheet 130in a convenient position away from the top of the vacuum apparatus 110.A suitable hanger assembly can be constructed from 0.25 inch (0.64 cm)diameter stainless steel rod. The latex dam sheet 130 is looped around adowel member 132 to facilitate grasping and to allow a convenientmovement and positioning of the latex dam sheet 130. In the illustratedposition, the dowel member 132 is shown supported in a hanger assembly128 to position the latex dam sheet 130 in an open position away fromthe top of the vacuum chamber 112.

A bottom edge of the latex dam sheet 130 is clamped against a rear edgesupport member 134 with suitable securing means, such as toggle clamps140. The toggle clamps 140 are mounted on the rear wall member 118 withsuitable spacers 141 which provide an appropriate orientation andalignment of the toggle clamps 140 for the desired operation. Threesupport shafts 142 are 0.75 inches (1.90 cm) in diameter and areremovably mounted within the vacuum chamber 112 by means of supportbrackets 144. The support brackets 144 are generally equally spacedalong the front wall member 116 and the rear wall member 118 andarranged in cooperating pairs. In addition, the support brackets 144 areconstructed and arranged to suitably position the uppermost portions ofthe support shafts 142 flush with the top of the front, rear and sidewall members of the vacuum chamber 112. Thus, the support shafts 142 arepositioned substantially parallel with one another and are generallyaligned with the side wall members 120 and 121. In addition to the rearedge support member 134, the vacuum apparatus 110 includes a frontsupport member 136 and two side support members 138 and 139. Each sidesupport member measures about 1 inch (2.54 cm) in width and about 1.25inches (3.18 cm) in height. The lengths of the support members areconstructed to suitably surround the periphery of the open top edges ofthe vacuum chamber 112, and are positioned to protrude above the topedges of the chamber wall members by a distance of about 0.5 inch (1.27cm).

A layer of egg crating type material 146 is positioned on top of thesupport shafts 142 and the top edges of the wall members of the vacuumchamber 112. The egg crate material extends over a generally rectangulararea measuring 23.5 inches (59.7 cm) by 14 inches (35.6 cm), and has adepth measurement of about 0.38 inches (0.97 cm). The individual cellsof the egg crating structure measure about 0.5 inch (1.27 cm) square,and the thin sheet material comprising the egg crating is composed of asuitable material, such as polystyrene. For example, the egg cratingmaterial can be McMaster Supply Catalog No. 162 4K 14, translucentdiffuser panel material. A layer of 6 mm (0.25 inch) mesh TEFLON®-coatedscreening 148, available from Eagle Supply and Plastics, Inc., inAppleton, Wis., U.S.A., which measures 23.5 inches (59.7 cm) by 14inches (35.6 cm), is placed on top of the egg crating material 146.

A suitable drain line and a drain valve 150 connect to bottom platemember 119 of the vacuum chamber 112 to provide a convenient mechanismfor draining liquids from the vacuum chamber 112. The various wallmembers and support members of vacuum apparatus 110 may be composed of asuitable noncorroding, moisture-resistant material, such aspolycarbonate plastic. The various assembly joints may be affixed bysolvent welding, and the finished assembly of the tester is constructedto be watertight. A vacuum gauge 152 operably connects through a conduitinto the vacuum chamber 112. A suitable pressure gauge is a Magnahelicdifferential gauge capable of measuring a vacuum of 0-100 inches ofwater (0-186 mmHg), such as a No. 2100 gauge available from DwyerInstrument Incorporated in Michigan City, Ind., U.S.A.

The dry product or other absorbent structure is weighed and then placedin excess 0.9% NaCl saline solution and allowed to soak for twentyminutes. After the twenty minute soak time, the absorbent structure isplaced on the egg crate material and mesh TEFLON®-coated screening ofthe Saturated Capacity tester vacuum apparatus 110. The latex dam sheet130 is placed over the absorbent structure(s) and the entire egg crategrid so that the latex dam sheet 130 creates a seal when a vacuum isdrawn on the vacuum apparatus 110. A vacuum of 0.5 pounds per squareinch (psi) (3.45 KPa) is held in the Saturated Capacity tester vacuumapparatus 110 for five minutes. The vacuum creates a pressure on theabsorbent structure(s), causing drainage of some liquid. After fiveminutes at 0.5 psi (3.45 KPa) vacuum, the latex dam sheet 130 is rolledback and the absorbent structure(s) are weighed to generate a wetweight.

The overall capacity of each absorbent structure is determined bysubtracting the dry weight of each absorbent from the wet weight of thatabsorbent, determined at this point in the procedure. The 0.5 psi (3.45KPa) SAT CAP or SAT CAP of the absorbent structure is determined by thefollowing formula:SAT CAP=(wet weight−dry weight)/dry weight;wherein the SAT CAP value has units of grams of fluid/gram absorbent.For both overall capacity and SAT CAP, a minimum of four specimens ofeach sample should be tested and the results averaged. If the absorbentstructure has low integrity or disintegrates during the soak or transferprocedures, the absorbent structure can be wrapped in a containmentmaterial such as paper toweling, for example SCOTT® paper towelsmanufactured by Kimberly-Clark Corporation, Neenah, Wis., U.S.A. Theabsorbent structure can be tested with the overwrap in place and thecapacity of the overwrap can be independently determined and subtractedfrom the wet weight of the total wrapped absorbent structure to obtain awet absorbent weight.

Functional Capacity Test Method

Functional capacity (grams/cc) is determined by dividing the actualsaturated capacity (grams liquid/gram foam) by the theoretical volumecapacity (cc liquid/gram foam). Theoretical volume capacity (“TVC”) isdetermined by the following formula (ref. Bland U.S. Pat. No. 6,071,580column 4 line 35):TVC=(1/Pf)*((1−Pf/Pp)*(% o.c./100)

where Pf is the density of the foam,

Pp is the density of the polymer, and

% o.c.=percent open cell content.

Fluid Intake Flux Test

The Fluid Intake Flux (FIF) Test determines the amount of time requiredfor an absorbent structure, and more particularly a foam sample thereof,to take in (but not necessarily absorb) a known amount of test solution(0.9 weight percent solution of sodium chloride in distilled water atroom temperature). A suitable apparatus for performing the FIF Test isshown in FIGS. 16A and 16B and is generally indicated at 200. The testapparatus 200 comprises upper and lower assemblies, generally indicatedat 202 and 204 respectively, wherein the lower assembly comprises agenerally 7 inch (18 cm) by 7 inch (18 cm) square lower plate 206constructed of a transparent material such as PLEXIGLAS® for supportingthe absorbent foam sample during the test and a generally 4.5 inch (11.4cm) by 4.5 inch (11.4 cm) square platform 218 centered on the lowerplate 206.

The upper assembly 202 comprises a generally square upper plate 208constructed similar to the lower plate 206 and having a central opening210 formed therein. A cylinder (fluid delivery tube) 212 having an innerdiameter of about one inch (2.54 cm) is secured to the upper plate 208at the central opening 210 and extends upward substantiallyperpendicular to the upper plate. For flux determination, the insidedimension of the fluid delivery tube should maintain a ratio between 1:3and 1:6 of the sample diameter. The central opening 210 of the upperplate 208 should have a diameter at least equal to the inner diameter ofthe cylinder 212 where the cylinder 212 is mounted on top of the upperplate 208. However, the diameter of the central opening 210 may insteadbe sized large enough to receive the outer diameter of the cylinder 212within the opening so that the cylinder 212 is secured to the upperplate 208 within the central opening 210.

Pin elements 214 are located near the outside comers of the lower plate206, and corresponding recesses 216 in the upper plate 208 are sized toreceive the pin elements 214 to properly align and position the upperassembly 202 on the lower assembly 204 during testing. The weight of theupper assembly 202 (e.g., the upper plate 208 and cylinder 212) isapproximately 360 grams to simulate approximately 0.11 pounds/squareinch (psi) (0.758 KPa) pressure on the absorbent foam sample during theFIF Test.

To run the FIF Test, an absorbent foam sample 207 being three inches indiameter is weighed and the weight is recorded in grams. The foam sample207 is then centered on the platform 218 of the lower assembly 204. Toprevent unwanted foam expansion into the central opening 210, centeredon top of the foam sample 207, is positioned an approximately 1.5 inchdiameter piece of flexible fiberglass standard 18×16 mesh window insectscreening 209, available from Phifer Wire Products, Inc., Tuscaloosa,Ala. The upper assembly 202 is placed over the foam sample 207 inopposed relationship with the lower assembly 204, with the pin elements214 of the lower plate 206 seated in the recesses 216 formed in theupper plate 208 and the cylinder 212 is generally centered over the foamsample 207. Prior to running the FIF test, the aforementioned SaturatedCapacity Test is measured on the foam sample 207. Thirty-three percent(33%) of the saturation capacity is then calculated; e.g., if the testfoam has a saturated capacity of 12 g of 0.9% NaCl saline testsolution/g of test foam and the three inch diameter foam sample 207weighs one gram, then 4 grams of 0.9% NaCl saline test solution(referred to herein as a first insult) is poured into the top of thecylinder 212 and allowed to flow down into the absorbent foam sample207. A stopwatch is started when the first drop of solution contacts thefoam sample 207 and is stopped when the liquid ring between the edge ofthe cylinder 212 and the foam sample 207 disappears. The reading on thestopwatch is recorded to two decimal places and represents the intaketime (in seconds) required for the first insult to be taken into theabsorbent foam sample 207.

A time period of fifteen minutes is allowed to elapse, after which asecond insult equal to the first insult is poured into the top of thecylinder 212 and again the intake time is measured as described above.After fifteen minutes, the procedure is repeated for a third insult. Anintake flux (in milliliters/second) for each of the three insults isdetermined by dividing the amount of solution (e.g., four grams) usedfor each insult by the intake time measured for the correspondinginsult. The intake rate is converted into a fluid intake flux bydividing by the area of the fluid delivery tube, i.e., 0.79 in² (5.1cm²).

At least three samples of each absorbent test foam is subjected to theFIF Test and the results are averaged to determine the intake time andintake flux of the absorbent foam.

Modified Fluid Intake Flux (FIF) Test for Smaller Foam Samples

The test is done in a similar same manner as described in theaforementioned standard Fluid Intake Flux (FIF) test; however, this testwas modified to accommodate smaller samples and yet keep the same fluiddelivery tube to sample size ratio as in the standard FIF test. Themodifications included installing the small sample of non-swelling foamthat is to be tested into a suitable holder and using a suitable fluiddelivery tube. The suitable holder can be an inverted laboratory glassfunnel having a uniform diameter cylindrical output tube of one inchlong that rests on top of an adjustable lab jack platform positioned fordownward gravitational flow. The foam, of sufficient diameter (between0.18 inch and 0.36 inch, or between 0.46 cm and 0.91 cm) and one inch(2.54 cm) in length, is gently positioned into the top of the uniformdiameter glass tube of the inverted funnel that is sufficient in size tohold the foam without significant compression so that one end facesvertically up (proximal end) and the other end is facing downward(distal end). The glass tube holds the foam in a stationary position andis sufficient in length to hold the foam sample yet then immediatelyenlarges to the funnel opening to avoid discharging flow complicationsof excess fluid after the fluid leaves the foam's distal end. A fluiddelivery tube is constructed with a 0.06 inch (0.15 cm) diameter orificeand a throat length that enlarges to a diameter enabling easydispensation of fluid into the tube. The enlargement occurs at anapproximately 0.25 inch (0.64 cm) length upstream of the orifice. Thefluid delivery tube is positioned directly above the proximal end of thefoam sample and the inverted funnel and the foam sample is raised usingthe lab jack such that the fluid delivery tube is brought into contactwith the foam. Afterwards, similar to the standard FIF test,thirty-three percent (33%) of the saturation capacity for the foamsample is then calculated and this volume of 0.9% NaCl saline solutionis dispensed using a PIPETMAN® P-200 μl pipette, available from Gilson,Inc. in Middleton, Wis., U.S.A., or similar pipette, into the fluiddelivery tube which measures 0.06 inches (0.15 cm) in discharge orificediameter, as opposed to a 1-inch (2.54 cm) diameter as described in thestandard FIF Test, and the rate of flow is measured with a stopwatch asearlier described. The preference is to utilize the earlier describedstandard FIF test rather than the Modified FIF test and, ifdiscrepancies exist, the standard FIF test is relied upon.

Vertical Wicking Test Method

A sample of foam is cut and mounted so that it hangs in a verticalorientation to gravity with an exposed foam edge in a substantiallyhorizontal orientation. A sufficiently large reservoir of 0.9% NaClsaline test solution is raised, using a standard lab jack, so that thefoam's horizontal edge extends approximately two millimeters beneath thesurface of the saline. A timer is started simultaneous to thepenetration of the foam into the saline. After thirty minutes, theheight of the fluid in the foam is measured relative to the surface ofthe saline. If desired, the saline can contain a non-surface active,non-chromatographic dye to aid in identifying the penetration andwicking of the test fluid within the foam. Alternatively, the foam maybe marked at the surface of the fluid and the fluid reservoir lowered toremove further contact with the foam. To compensate for possible foamexpansion upon hydration, the foam may be marked at the fluid surfaceafter the wicking time. Measurement of the fluid height in the foamusing the initial foam dimensions may be done via appropriate meansincluding x-ray imaging, optical measurement, or slicing sections of thefoam until 0.9% NaCl saline test solution is apparent in the slice. Forexample in Sample 3d, the vertical wicking height was measured byoptical methods and confirmed with x-ray imaging. Sample 3d did notexpand; therefore, compensating for expansion was not necessary.

Surfactant Permanence Test

The Surfactant Permanence Test is based upon the surface tensiondepression effect by surfactant addition to water. The surface tensionis measured by the duNoüy ring tensiometer method utilizing a KrüssProcessor Tensiometer—K 12 instrument, available from Krüss USA inCharlotte, N.C., U.S.A. In general terms, a sample of foam is soaked indistilled water and the surface tension of the supernatant is measured.This surface tension is compared to a calibration curve to determine theamount of surfactant washed from the foam.

Test preparation includes creating a calibration curve for theparticular surfactant utilized. This curve shows the reduced surfacetension of the solution as surfactant concentration increases. Atconcentrations above the critical micelle concentration (CMC), thesurface tension reduction from additional surfactant is minimal.

A sample of pre-weighed foam is placed in distilled water. The sample isimmersed in the room temperature water for 24 hours, allowing fugitivesurfactant to leach out of the foam and dissolve into the water. Theamount of water used is critical. If the amount of surfactant leachedinto the water creates a concentration greater than the CMC, measurementof surface tension on the solution will only indicate that theconcentration is greater than the CMC. The amount of distilled waterused to wash the foam is 100 times the weight of the foam. After the24-hour soak, the foam is removed from the water/surfactant solution(supernatant). The water in the foam is allowed to drain into thesupernatant and gentle pressure is applied to the foam to aid in theremoval of excess supernatant in the foam. The surface tension of thetotal supernatant is then measured. Utilizing the calibration curve, thesurface tension corresponds to a weight fraction of surfactant in thewater. This weight fraction is then multiplied by the total amount ofwater to yield the weight of surfactant leached from the foam. Theamount of surfactant removed can be expressed as a fraction of the totalsurfactant in the initial foam. For example: foam is made with 10 partssurfactant for every 90 parts foam. A 100 gram sample is soaked in10,000 grams of distilled water. The surface tension measurement of thesupernatant indicates that the surfactant concentration in thesupernatant is 0.03%. The amount of surfactant dissolved from the foamis 3.0 grams. The amount of surfactant in the initial foam was 10 grams,so 30% of the surfactant was dissolved and 70% of the surfactant remainsin the foam.

With Clariant HOSTASTAT® HS-1, the CMC is at a concentration of 0.03%,by weight. At concentrations less than the CMC, the surface tension isdescribed by: σ=5 ln([s])−18 where σ is the surface tension and [s] isthe weight fraction of the surfactant. As an example, 2.96 grams of anopen-cell polystyrene foam made with 2.5 parts HOSTASTAT® HS-1 to 100parts polystyrene was immersed in 297.79 grams of distilled water for 24hours. The surface tension of the supernatant was measured at 39dynes/cm which corresponds to 0.0027 grams of surfactant dissolved intothe water, or 3.7% of the total surfactant; therefore, 96.3% of thesurfactant remained in the foam after a 24 hour wash.

Viscous Fluid Saturated Capacity and Retention Capacity Test

The saturation capacity and the retention capacity can be determined bysoaking a 3.81 cm×3.81 cm×2 mm (a comparable 14.5 square centimetersurface area if smaller samples are tested, and if thicker samples areused, they will need to be sliced down using conventional non-densifyingmeans) sample of absorbent foam in approximately 30 milliliters of amenses simulant test fluid (described below) in a plastic dish that issufficient to fully saturate the sample for thirty minutes. Thepre-weighed foam is placed on a strip of scrim-like material (for samplehandling), then placed into the 30 milliliters of test fluid making surefluid completely covers the sample. The dish is covered so evaporationdoes not occur. While soaking thirty minutes, the test fluid amount ismonitored so that there is always excess fluid. The foam sample is thenremoved using the scrim and placed between two pieces of approximately4-inch (10 cm) by 4-inch (10 cm) through-air-bonded-carded web materialand on the outside of this sandwich; a layer of approximately 4-inch (10cm) by 4-inch (10 cm) blotter paper is positioned on each side such thatthe blotter paper is facing the outside. A description of thesematerials is provided below. A pressure of 0.05 psi (0.345 KPa or 0.035N/cm²) is applied for five minutes to remove any pools of liquid. Thesaturated sample is then weighed. The weight of the liquid held in thefoam sample divided by the dry weight of the foam sample is thesaturation capacity of the sample.

After the saturated foam sample is weighed, the absorbent foam sample isplaced in a centrifuge and spun at 300 G for three minutes so that thefree fluid is discharged. The spun foam sample is then weighed. Theweight of the liquid remaining in the spun foam sample divided by thedry weight of the sample is the retention capacity of the foam sample.

Accordingly:

-   -   a. Saturation Capacity=(Wet Wt. Before Centrifuge−Dry Wt.)/(Dry        Wt.)    -   b. Retention Capacity=(Wet Wt. After Centrifuge−Dry Wt.)/(Dry        Wt.)

A suitable through-air-bonded-carded web material has a 2.5 osy (84.8g/m²) basis weight, a 0.024 g/cm³ density, and is composed of 60 wt % of6 denier, KoSa type 295 polyester fiber; and 40 wt % of 3 denier, ChissoESC-HR6 bicomponent fiber. The polyester fiber is available from KoSa, abusiness having offices located in Charlotte, N.C., U.S.A., and thebicomponent fiber is available from Chisso Corporation, a businesshaving offices located in Osaka, Japan. A suitable blotter paper is100-lb VERIGOOD white blotter paper available from Georgia PacificCorporation, a business having offices located in Menasha, Wis., U.S.A.(e.g. product item number 411 01012). Substantially equivalent materialsmay optionally be employed.

The “menses simulant” test fluid is composed of swine blood diluted withswine plasma to provide a hematocrit level of 35% (by volume). Asuitable device for determining the hematocrit level is a HEMATOSTAT-2system, available from Separation Technology, Inc., a business havingoffices located in Altamonte Springs, Fla., U.S.A. A substantiallyequivalent system may alternatively be employed.

Edge Compression Test Method

The method by which the Edge-wise Compression (EC) value can bedetermined is set forth below. A 2-inch by 12-inch (5.1 cm by 30.5 cm)piece of absorbent foam is used. The weight of the sample is determined.The thickness of the material is measured using a hand micrometer whileavoiding surface compression. The material is formed into a cylinderhaving a height of 2 inches (5.1 cm), and with the two ends having0-0.125 inch (0-3.18 mm) overlap, the material is stapled together withthree staples. One staple is near the middle of the width of theproduct, the other two nearer each edge of the width of the material.The longest dimension of the staple is in the circumference of theformed cylinder to minimize the effect of the staples on the testing.

A tensile tester, such as those commercially available from MTS SystemsCorporation in Eden Prairie, Minn., U.S.A., is configured with a bottomplatform, a platen larger than the circumference of the sample to betested and parallel to the bottom platform, attached to a compressionload cell placed in the inverted position. The specimen is placed on theplatform under the platen. The platen is brought into contact with thespecimen and compresses the sample at a rate of 25 mm./min. The maximumforce obtained in compressing the sample to 50% of its width (1 inch)(2.54 cm) is recorded.

Bucking of the material is identified as a maximum in the compressionforce and is typically observed before the material is compressed to 50%of its uncompressed length. In a product where the length of theabsorbent is less than 12 inches (30.5 cm), the EC value of the materialcan be determined in the following manner. Based on theoretical modelsgoverning buckling stresses, in the Edge-wise Compression configurationdescribed, the buckling stress is proportional to E*t²/(H²) with theproportionality constant being a function of H²/(R*t) where E is theElastic modulus, H is the height of the cylinder, R is the radius of thecylinder, and t is the thickness of the material. Expressing the stressin terms of force per basis weight, it can be shown that the parameterthat needs to be maintained constant is H²/R. Therefore, for a samplethat is smaller than 12 inches (30.5 cm), the largest possible circleshould be constructed and its height (width of the sample being cut out)adjusted such that H²/R equals 2.1 inches (5.3 cm). A detaileddiscussion of edge-wise compression strength has been given in TheHandbook Of Physical And Mechanical Testing Of Paper And Paperboard,Richard E. Mark editor, Dekker 1983 (Vol. 1).

Vertical Wicking Fluid Flux

Definition

The vertical wicking fluid flux is the rate of change of fluid mass thatmoves vertically against gravity into an absorbent material per unit ofcross sectional area. In general the fluid flux changes as a function ofdistance from the surface of the fluid. While vertical wicking fluidflux can be defined and measured at various heights/distances from thefluid surface this testing was done at a zero height. In this way it isnot necessary to measure the distance the fluid has moved as a functionof time. It remains only to measure the time rate of change of fluidmass being absorbed into the sample and divide that by the crosssectional area of the material.

Equipment: Apparatus 300 (FIG. 19) including the following:

1. Balance 302 accurate to at least 0.01 g and capable of communicationwith a computer. Connecting hooks 304 connect the sample holding fixture306 to the balance 300.

2. Computer and software to record mass as a function of time accurateto 0.1 seconds.

3. Translational stage 318 capable of at least 2″ vertical travel. Thestage needs to move a platform 319 in the vertical direction withminimal (<1mm) motion in the horizontal plane as the stage 318 moves. Asuitable platform is 12.7 cm×12.7 cm. One electronic stage is sold byVelmex Inc. of Bloomfield, N.Y. as the translational stage model#ZMH2504W1-S2.5-FL-BK with a stepper motor and controller model VXM-1.

4. Clear acrylic tube 312. Tube is 12.7 cm OD and 5.7 cm ID. The tubeshould be 25.4 cm in height.

5. Tube Cover. An acrylic top that is a cylinder 1.9 cm thick with 6.35cm outer diameter. A lip is cut so the cover fits part way into thetube. The lip is 0.64 cm deep in the thickness direction, and 0.38 cmdeep in the radius direction. In the center of the cover a through holeis cut with a 0.32 cm diameter. See the drawings below.

6. Lab jack 322.

Test method:

1. Ensure the balance 302 is aligned so that holding mechanism 306 doesnot touch the tube 312.

2. Cut test material to 6″×1″ (15 cm×2.5 cm) strips such that the longaxis is aligned with the desired direction of the fluid flow.

3. Weigh the sample. Measure the caliper of the sample to the nearest0.05 mm with a pressure of (0.345 KPa).

4. Place sample 308 into clip in the sample holding mechanism 306.

5. Place the sample 308, the holding mechanism 306 and the samplechamber lid 310 onto the sample chamber tube 312.

6. Fill the beaker 314 with 20 ml of test fluid 316. Use 1% saline with1 drop blue food coloring per 250 ml of fluid. Place the beaker 314 onthe translational stage 318, which is controlled with a stepper motor320.

7. Place the sample holding chamber 315 over the beaker 314 taking carenot to allow the sample 318 to contact the fluid 316. If necessaryadjust the sample holder 306 to get the sample 318 to be held verticallywithout contact with the beaker wall.

8. Connect the sample holding assembly 306 to the balance at theconnecting hook.

9. Adjust the translational stage 318 and or lab jack 322 so that thesample 318 is approximately 2 mm above the surface of the fluid 316.Ensure that there is enough remaining travel in the translational stage318 to move the beaker 314 and fluid 316 into contact with the sample308.

10. Adjust the location of the sample chamber 315 so that the wire fromthe sample holder 306 is not in contact with either the vertical samplechamber lid 310 or the hole in the table 303 connecting to the wire tothe balance 302.

11. Tare the balance 302.

12. Set up the computer to record the mass every second for 1800seconds.

13. Move the translational stage 318 so the bottom edge of the sample isbelow the surface of the fluid by 2 mm. This must be done within 5seconds.

14. If the sample 308 absorbs enough fluid 316 that the sample 308 isnot in contact with the fluid 316 then the data is not valid. Re-run thesample so that the sample is submerged 4 mm instead of 2 mm.

15. Measure the maximum distance fluid has moved vertically, subtractingthe distance the material was submerged into the fluid.

16. Measure the caliper 2 mm above the bottom edge of the sample 308.The caliper measurement should be done at 0.05 psi (0.345 KPa).

Data Analysis:

1. Using the data recorded calculate the time rate of change of fluidmass at 1000 seconds.

2. Using the sample width (2.54 cm) and the sample caliper calculate thecross sectional area.

3. Calculate the fluid flux at zero height by dividing the mass flowrate from step 1 by the cross sectional area calculated in step 2.Ensure the correct units.

It is recognized that some foams with hydration will swell and grow andtherefore change in physical dimensions with fluid wicking. Significantchanges in the cross-sectional area need to be accounted for in order tomeasure an accurate fluid flux. In addition, any significant change inthe length of the foam as fluid is wicked will alter the location of thezero height position above the fluid reservoir. For these reasons,changes in the setup and test procedure may be required to accommodatesuch swellable foams. Such changes will be apparent to persons skilledin the art. An example of such a material is a polyurethane foamproduced by Rynel Ltd., Boothbay, Me., and sold as Rynel 562-B.

While the embodiments of the invention disclosed herein are presentlypreferred, various modifications and improvements can be made withoutdeparting from the spirit and scope of the invention. The scope of theinvention is indicated by the appended claims, and all changes that fallwithin the meaning and range of equivalents are intended to be embracedtherein.

1. A thermoplastic absorbent foam, comprising: a base resin; asurfactant; and a plasticizing agent; the foam having an open cellcontent of about 50% or greater, a density of about 0.10 grams/cm³ orless, a saturated capacity of about 3 grams/gram or greater measuredunder a load of 3.45 KPa, and a bending modulus of less than about 6000KPa at 1 mm deflection.
 2. The foam of claim 1, wherein the base resincomprises at least one of the group consisting of polystyrene, styrenecopolymers, polyolefins, polyesters, and combinations thereof.
 3. Thefoam of claim 1, further comprising between about 10% and about 50%thermoplastic elastomer, by weight, of the foam.
 4. The foam of claim 3,wherein the thermoplastic elastomer comprises at least one of the groupconsisting of styrenic block copolymers including diblock and triblockcopolymers which may include styrene-isoprene-styrene (SIS),styrene-butadiene-styrene (SBS), styrene-isoprene-butadiene-styrene(SIBS), styrene-ethylene/butylene-styrene (SEBS),styrene-ethylene/propylene-styrene (SEPS); polyolefin-basedthermoplastic elastomers including random block copolymers includingethylene α-olefin copolymers; block copolymers including hydrogenatedbutadiene-isoprene-butadiene block copolymers; stereoblockpolypropylenes; graft copolymers, including ethylene-propylene-dieneterpolymer (EPDM), ethylene-propylene random copolymers (EPM) andethylene propylene rubbers (EPR); blends of thermoplastic elastomerswith dynamic vulcanized elastomer-thermoplastic blends; thermoplasticpolyether ester elastomers; ionomeric thermoplastic elastomers;polyamide thermoplastic elastomers; thermoplastic polyurethanes; andcombinations thereof.
 5. The foam of claim 1, wherein the surfactantcomprises an anionic surfactant.
 6. The foam of claim 1, wherein thesurfactant comprises a multi-component surfactant system
 7. The foam ofclaim 1, wherein the plasticizing agent comprises at least one of thegroup consisting of polyethylene; ethylene vinyl acetate; mineral oil,palm oil, waxes, naphthalene oil, paraffin oil, acetyl tributyl citrate;acetyl triethyl citrate; p-tert-butylphenyl salicylate; butyl stearate;butylphthalyl butyl glycolate; dibutyl sebacate; di-(2-ethylhexyl)phthalate; diethyl phthalate; diisobutyl adipate; diisooctyl phthalate;diphenyl-2-ethylhexyl phosphate; epoxidized soybean oil; ethylphthalylethyl glycolate; glycerol monooleate; monoisopropyl citrate; mono-, di-,and tristearyl citrate; triacetin (glycerol triacetate); triethylcitrate; 3-(2-xenoyl)-1,2-epoxypropane; and combinations thereof.
 8. Thefoam of claim 1, wherein the plasticizing agent comprises athermoplastic elastomer.
 9. The foam of claim 1, wherein the foam has afluid intake flux of about 0.15 ml/sec/cm² or greater upon the firstinsult, about 0.15 ml/sec/cm² or greater upon the second insult, andabout 0.15 ml/sec/cm² or greater upon the third insult.
 10. The foam ofclaim 1, wherein the foam has a cross-direction trap tear strength ofabout 200 grams or greater and a machine-direction trap tear strength ofabout 400 grams or greater.
 11. The foam of claim 1, wherein the foamhas a peak load edge compression of about 1000 grams or less.
 12. Thefoam of claim 1, wherein the foam has a compression resistance of about20% compression set or less.
 13. The foam of claim 1, wherein the foamhas a vertical wicking height of about 5 cm or greater.
 14. The foam ofclaim 1, wherein the bending modulus is less than about 4000 KPa at 1 mmdeflection.
 15. The foam of claim 1, wherein the bending modulus is lessthan about 2000 KPa at 1 mm deflection.
 16. An absorbent articlecomprising the foam of claim
 1. 17. The absorbent article of claim 16,wherein the article is selected from the group consisting of personalcare articles, household/industrial articles and health/medicalarticles.
 18. A roll product comprising a foam sheet wound into a roll,wherein the foam sheet comprises the foam of claim
 1. 19. Athermoplastic absorbent foam, comprising: about 45 to about 90% byweight of a base resin; about 10 to about 55% by weight of athermoplastic elastomer; and about 0.05 to about 10% by weight of asurfactant; wherein the foam has an open cell content of about 50% orgreater, a fluid intake flux of about 0.15 ml/sec/cm² or greater, and abending modulus of less than about 6000 KPa at 1 mm deflection.
 20. Thefoam of claim 19, further comprising about 0.5% to about 10% by weightof an additional plasticizing agent.
 21. The foam of claim 19, whereinthe thermoplastic elastomer comprises a styrenic block copolymerincluding at least one of the group consisting ofstyrene-isoprene-styrene (SIS), styrene- butadiene-styrene (SBS),styrene-isoprene-butadiene-styrene (SIBS),styrene-ethylene/butylene-styrene (SEBS),styrene-ethylene/propylene-styrene (SEPS), and combinations thereof. 22.The foam of claim 21, wherein the thermoplastic elastomer has a diblockcontent between about 50% and about 80% of a total weight of thethermoplastic elastomer.
 23. The foam of claim 19, wherein the bendingmodulus is less than about 4000 KPa at 1 mm deflection.
 24. The foam ofclaim 19, wherein the bending modulus is less than about 2000 KPa at 1mm deflection.
 25. The foam of claim 19, comprising a vertical wickingfluid flux at zero height of at least about 5 g/sec/m².
 26. The foam ofclaim 19, comprising a functional capacity greater than about 0.2cc/gram.
 27. The foam of claim 19, comprising a compression resistanceof about 20% compression set or less.
 28. The foam of claim 19,comprising a density of less than about 0.07 g/cm³.
 29. The foam ofclaim 19, comprising a density of about 0.02 g/cm³ to about 0.10 g/cm³.30. The foam of claim 19, comprising a saturated capacity of about 3 g/gto about 9 g/g, as measured under a 3.45 KPa loading.
 31. The foam ofclaim 19, comprising a wet tensile loss of less than about 10% in amachine direction and in a cross direction.
 32. The foam of claim 19,comprising a static coefficient of friction of about 0.4 to about 1.0.33. An absorbent article comprising the foam of claim
 19. 34. Theabsorbent article of claim 33, wherein the article is selected from thegroup consisting of personal care articles, household/industrialarticles and health/medical articles.
 35. A roll product comprising afoam sheet wound into a roll, wherein the foam sheet comprises the foamof claim
 19. 36. A thermoplastic absorbent foam, comprising: betweenabout 40% and about 80% by weight of a polystyrene base resin andbetween about 20% and about 60% by weight of a styrene block copolymerthermoplastic elastomer, wherein the absorbent foam has an open cellcontent of about 50% or greater, a bending modulus less than about 6000KPa at 1 mm deflection, and a density of about 0.10 grams/cm³ or less.37. An absorbent article comprising the foam of claim
 36. 38. Theabsorbent article of claim 37, wherein the article is selected from thegroup consisting of personal care articles, household/industrialarticles, and health/medical articles.
 39. A roll product comprising afoam sheet wound onto a roll, wherein the foam sheet comprises the foamof claim 36.